Composite material having ceramic fibers

ABSTRACT

The present disclosure provides a composite material, a method of making and using the composite material and dental products made by hardening the composite material. The composite material includes a polymerizable component, ceramic fibers and nanoclusters. Each of the ceramic fibers of the composite material has a length and where the length of fifty percent of the ceramic fibers, based on a total number of the ceramic fibers, is at least 50 micrometers and the length of ninety percent of the ceramic fibers, based on the total number of the ceramic fibers, is no greater than 500 micrometers. The composite material can also include discrete non-fumed metal oxide nanoparticles. The composite material can be hardened to become any one of a dental restorative, a dental adhesive, a dental mill blank, a dental cement, a dental prostheses, an orthodontic device, an orthodontic adhesive, a dental casting material or a dental coating.

TECHNICAL FIELD

The present disclosure provides for a composite material, and moreparticularly a composite material having ceramic fibers.

BACKGROUND

Direct dental restorative materials consist of a curable phase,typically a methacrylate resin, an initiator and a filler system. Thesematerials are typically highly filled with particulate such as nanoscaleparticles, micrometer milled materials and/or solution grown inorganics.Furthermore, similar compositions made from pre-cured “composites”(e.g., dental mill blanks) have been introduced to the market, where thematerial is cured out of the mouth and shaped into a final restorativeshape (e.g., inlay, onlay or crown) via a reduction process (e.g.,milling). All of these dental restorative materials have requirementsthat include high strength, stiffness, and fracture toughness tofunction in the oral environment. Especially in large posteriorrestorations, a higher fracture toughness material is highly desirable.

Attempts have been made to include fibers in dental restorativematerials in order to improve their mechanical properties. However, thishas come at a cost to handling and aesthetic characteristics. The use offibers unfortunately creates a stiff, “crunchy” type of handling that isdifficult to work with (e.g., shape, and feather). Once cured, thesurfaces of these dental restorative materials rapidly lose their glosswith every day wear. Additionally, many of these dental restorativematerials produce a highly opaque material due to refractive indexmismatch between the fiber and the resin. This refractive index mismatchresults in a less than desirable aesthetic result.

As such, there is a need in the art for a composite material thatincludes fibers, where the composite material is easy to handle andprovides good aesthetics properties while still providing the necessarymechanical properties for use as a dental restorative material.

SUMMARY

The present disclosure provides a composite material having improvedhandling properties along with good aesthetic qualities while stillproviding the necessary mechanical properties for use as a dentalrestorative material. Specifically, the composite material includes 20to 40 weight percent (wt. %) of a polymerizable component; 4 to 50 wt. %of ceramic fibers; and 20 to 70 wt. % of nanoclusters, where the wt. %values of the composite material are based on a total weight of thecomposite material and total to a value of 100 wt. %. Each of theceramic fibers has a length, where the length of fifty percent of theceramic fibers, based on a total number of the ceramic fibers, is atleast 50 micrometers and the length of ninety percent of the ceramicfibers, based on the total number of the ceramic fibers, is no greaterthan 500 micrometers. The highly uniform length of the ceramic fibersalong with the nanoclusters surprisingly results in improvements to boththe handling properties of the composite material and upon hardening themechanical properties of the hardened composite material. In addition,the aesthetic properties achieved by the composite material allow for,among other things, a polish on a surface of the composite material tobe retained even after repetitive abrasive contact.

The composite material can include up to 12 wt. % of nanoparticles basedon the total weight of the composite material. For example, thecomposite material can include 2 to 12 wt. % of nanoparticles based onthe total weight of the composite material. The nanoparticles can bediscrete non-fumed metal oxide nanoparticles. Discrete non-fumed metaloxide nanoparticles can be discrete non-fumed heavy metal oxidenanoparticles. The discrete non-fumed metal oxide nanoparticles can alsoinclude both discrete non-fumed heavy metal oxide nanoparticles anddiscrete non-fumed non-heavy metal oxide nanoparticles. The compositematerial can also include 22 to 64 wt. % of nanoclusters, as discussedherein.

A variety of physical properties are possible for the ceramic fibers ofthe present disclosure. For example, the length of sixty-five percent ofthe ceramic fibers, based on a total number of the ceramic fibers, canbe at least 100 micrometers and the length of ninety percent of theceramic fibers, based on the total number of the ceramic fibers, can beno greater than 350 micrometers. The ceramic fibers can have anarithmetic mean length of 50 micrometers to 500 micrometers, preferablythe ceramic fibers can have an arithmetic mean length of 100 micrometersto 170 micrometers. The ceramic fibers can also have an arithmetic meandiameter of 0.5 to 20 micrometers. In one embodiment, the arithmeticmean diameter of the ceramic fibers can be 9 to 12 micrometers.

The ceramic fibers can be amorphous ceramic fibers. In one embodiment,the ceramic fibers are formed with aluminum oxide and silicon dioxideand have less than 14 weight percent of boron trioxide based on thetotal weight of the ceramic fibers. Examples, of such ceramic fibers canhave a surface area of at least 10 square meters per gram (m²/g).

The polymerizable component of the composite material can form ahardened polymerizable component having a refractive index. As discussedherein, the refractive index of the hardened polymerizable component isclosely matched to the refractive index of the ceramic fibers. Forexample, the ceramic fibers can have a refractive index value within 0.1or less of the refractive index of the hardened polymerizable component.In an additional embodiment, the polymerizable component can form ahardened polymerizable component having a refractive index, where theceramic fibers have a refractive index value within 0.05 or less of therefractive index of the hardened polymerizable component. Examples ofrefractive index values for the ceramic fibers include ceramic fibershave a refractive index value of 1.40 to 1.65. In an additional example,the refractive index value of the ceramic fibers is 1.50 to 1.58.

For the various embodiments, the polymerizable component can be anethylenically unsaturated compound. The polymerizable component canfurther include an initiator selected from the group consisting of afree radical initiator, a photoinitiator, a thermally activatedinitiator or a combination thereof.

The composite material of the present disclosure can be hardened to makea dental product. The dental product can be selected from the groupconsisting of a dental restorative, a dental adhesive, a dental millblank, a dental cement, a dental prostheses, an orthodontic device, anorthodontic adhesive, a dental casting material, artificial crowns,anterior fillings, posterior fillings, and cavity liners or a dentalcoating. The composite material of the present disclosure can also beused near or on a tooth surface. For example, the composite material canbe placed near or on a tooth surface, where the shape of the compositematerial near or on the tooth surface can be changed prior to hardeningthe composite material. Changing the shape of the composite materialnear or on the tooth surface can include shaping the composite materialinto a dental product selected from the group consisting of a dentalprosthesis, an orthodontic device, a dental crown, an anterior filling,a posterior filing or a cavity liner. After hardening, the compositematerial can be polished. The nanoclusters of the composite material canbe silica-zirconia nanoclusters.

Examples of such silica-zirconia nanoclusters include those formed byprimary particles, where each of the primary particles has a diameter of1 nanometer to 200 nanometers, where the primary particles forming thesilica-zirconia nanocluster are grouped together in a cluster formation.Such nanoclusters may be substantially amorphous. Such nanoclusters maycontain crystalline phases (e.g., zirconia) within them.

The present disclosure further includes a method of making the compositematerial, where the method includes providing 20 to 40 wt. % of thepolymerizable component, providing 4 to 50 wt. % of ceramic fibers, andproviding 20 to 70 wt. % of nanoclusters, where the wt. % values of thecomposite material are based on a total weight of the composite materialand total to a value of 100 wt. %., where each of the ceramic fibers hasa length and where the length of fifty percent of the ceramic fibers,based on a total number of the ceramic fibers, is at least 50micrometers and the length of ninety percent of the ceramic fibers,based on the total number of the ceramic fibers, is no greater than 500micrometers; and admixing the polymerizable component, the ceramicfibers and the nanoclusters to make the composite material. The methodcan also include providing up to 12 wt. % of nanoparticles based on thetotal weight of the composite material, and admixing the polymerizablecomponent, the ceramic fibers and the nanoclusters and the nanoparticlesto make the composite material.

The ceramic fibers of the present disclosure can also be treated inorder to modify their surface properties. For example, the ceramicfibers can include a surface area, where the method includes treatingthe ceramic fibers to change the surface area of the ceramic fibers. So,for example, the ceramic fibers can include a predetermined amount ofboron trioxide where treating the ceramic fibers to change the surfacearea of the ceramic fibers includes removing at least a portion of theboron trioxide from the ceramic fibers. Removing at least a portion ofthe boron trioxide can include boiling the ceramic fibers in water toremove the boron trioxide in the ceramic fibers.

The present disclosure further includes a method of using the compositematerial of the present disclosure, where the method includes placingthe composite material of the present disclosure near or on a toothsurface; changing the shape of the composite material near or on thetooth surface; and hardening the composite material. Finally, thepresent disclosure provides a kit that includes the composite materialas provided herein and at least one container to hold the compositematerial.

DETAILED DESCRIPTION

The present disclosure provides a composite material having improvedhandling properties along with good aesthetic qualities while stillproviding the necessary mechanical properties for use as a dentalrestorative material. Specifically, the composite material includes apolymerizable component, ceramic fibers and nanoclusters. The ceramicfibers used in the composite material, as discussed herein, have ahighly uniform length. The highly uniform length of the ceramic fibersalong with the use of the nanoclusters surprisingly results inimprovements to both the handling properties of the composite materialand upon hardening the aesthetics properties of the hardened compositematerial. Examples of such improved aesthetics properties includehardened composite materials that are able to retain their polish evenafter exposure to repetitive abrasion, such as through brushing withtoothpaste.

The hardened composite material of the present disclosure may also haveother desirable aesthetic, physical and mechanical properties. Forexample, the hardened composite material of the present disclosure canhave radiopacity, high mechanical strength and a substantialtranslucency. Radiopacity is a very desirable property for a compositematerial used in dental applications. Being radiopaque allows thecomposite material to be examined using standard dental X-ray equipment,thereby facilitating long term detection of marginal leakage or cariesin tooth tissue adjacent to the hardened composite material.

The hardened composite material can have a substantial translucency(e.g., a low visual opacity) to visible light. Having translucency isdesirable so that the hardened composite material will have a life-likeappearance when used as a dental restorative material. If such acomposite material is intended to be hardened or polymerized usingvisible light-induced photoinitiation, translucency is desirable inorder to reach the depth of cure required (sometimes as much as twomillimeters or more), to accomplish uniform hardness in the hardenedcomposite material, and to respond to the physical limitations imposedby carrying out the hardening reaction within the mouth (which require,among other things, that the unhardened composite material usually beexposed to light from limited angles, and that the hardening radiationbe provided by a portable instrument). The translucency can be achievedfor the composite material, as discussed herein, in part by matching therefractive index of the ceramic fibers with the refractive index of thehardened polymerizable component of the composite material.

Practitioners also desire good handling properties in a compositematerial used for dental applications, as this property translates totime savings. For example, in dental restorative work, it is desirablethat the composite material be easily shaped, contoured and featheredinto the desired shape. Until the present disclosure, attempts at usingfibers in composite materials at loadings levels sufficient to improvethe mechanical properties made the handling of the composite materialpoor at best. Such attempts with ground or milled fibers created a“crunchy” type of handling, which is something to avoid for a dentalrestorative material to have good handling and “featherability”characteristics. These other composite materials also had “lumps,” whichmakes for unpredictable and non-uniform handling of the material.

Unlike these failed attempts, the composite material of the presentdisclosure maintains good handling characteristics at fiber loadingssufficient to improve the mechanical properties. The composite materialof the present disclosure displays a consistent and uniform composition,which allows for predictable and uniform handling of the compositematerial. In addition, the refractive index of the ceramic fibers andthe polymerizable component used in the present disclosure are suitablymatched so as to provide substantial translucency (e.g., low visualopacity) and high aesthetic quality for use as a dental restorativematerial. Finally, the hardened composite material of the presentdisclosure displays enhanced fracture toughness and flexural modulus dueto the presence of the ceramic fibers and the nanoclusters, with minimaldegradation of handling or aesthetic properties of the compositematerial. This is unexpected, as the use of fibers is known to decreaseboth handling and aesthetic properties of composite materials.

While not wishing to be bound by theory, it is hypothesized that it is acombination of the size and relatively uniform distribution of theceramic fibers and the nanoclusters used in the composite material ofthe present disclosure that is leading to these favorable attributes.The highly uniform length of the ceramic fibers surprisingly results inimprovements to both the handling properties of the composite materialand upon hardening the physical properties of the hardened compositematerial. Examples of such improved physical properties include dentalrestorative materials that are able to retain their polish afterrepetitive abrasive contact.

Definitions

As used herein, a “ceramic” is a rigid material that consists of aninfinite three-dimensional network comprising metals bonded to carbon,nitrogen or oxygen. The ceramic, as used herein, may be crystalline,partially crystalline or amorphous.

The term “electron donor” generally refers to a compound that has asubstituent that can donate electrons. Suitable examples include, butare not limited to, a primary amino, secondary amino, tertiary amino,hydroxy, alkoxy, aryloxy, alkyl, or combinations thereof.

As used herein, “hardenable” is descriptive of a material or compositionthat can be cured (e.g., polymerized or crosslinked) or solidified, forexample, by removing solvent (e.g., by evaporation and/or heating);heating to induce polymerization and/or crosslinking; irradiating toinduce polymerization and/or crosslinking; and/or by mixing one or morecomponents to induce polymerization and/or crosslinking.

By “dental product” is meant an article that can be adhered (e.g.,bonded) to an oral surface (e.g., a tooth structure). Typically, adental product is a restored dentition or a portion thereof. Examplesinclude restoratives, replacements, inlays, onlays, veneers, full andpartial crowns, bridges, implants, implant abutments, copings, anteriorfillings, posterior fillings, cavity liners, sealants, dentures, posts,bridge frameworks and other bridge structures, abutments, orthodonticappliances and devices, and prostheses (e.g., partial or full dentures).

As used herein, “sizing” is defined as starch, oil, wax or othersuitable ingredients (e.g., an organic ingredient) applied to a fiberstrand to protect and aid handling. A sizing contains ingredients toprovide lubricity and binding action. Sizing may also encompass surfacetreatments, for example with a silane, where the silane may include areactive group, for example a polymerizable group.

By “oral surface” is meant a soft or hard surface in the oralenvironment. Hard surfaces typically include tooth structure including,for example, natural and artificial tooth surfaces, bone, tooth models,dentin, enamel, cementum, and the like

By “filler” is meant a particulate material suitable for use in the oralenvironment. Dental fillers generally have a number average particlesize diameter of at most 100 micrometers.

By “contouring” refers to the process of shaping a material (usingdental instruments) so that it resembles the natural dental anatomy. Foreasy contouring, materials should have a sufficiently high viscositythat they maintain their shape after manipulation with a dentalinstrument, and yet the viscosity should not be so high that it isdifficult to shape the material.

By “feathering” refers to the process of reducing the dental restorativematerial to a thin film in order to blend the material into the naturaldentition. This is done with a dental instrument at the margin of themanipulated material and the natural dentition.

By “amorphous ceramic fibers” is meant a non-crystalline solid thatlacks the long-range order characteristic of a crystal. As used herein,“amorphous ceramic fibers” are synonymous with glass.

As used herein, “nanoparticles” are discrete non-fumed metal oxidenanoparticles. Discrete non-fumed metal oxide nanoparticles can befurther classified as either “discrete non-fumed non-heavy metal oxidenanoparticles” or “discrete non-fumed heavy metal oxide nanoparticles.”The “discrete non-fumed non-heavy metal oxide nanoparticles” means anoxide of elements other than those of heavy metals (which are definedherein as the “discrete non-fumed heavy metal oxide nanoparticles”). Asused herein, “non-heavy metal oxide” means a metal oxide of elementshaving an atomic number of no greater than 28. In one aspect of thedisclosure, silica is an example of a non-heavy metal oxide and silicananoparticles are an example of discrete non-fumed non-heavy metal oxidenanoparticles. As used herein, “heavy metal oxide” means an oxide ofelements having an atomic number greater than 28. In one aspect of thedisclosure, zirconium oxide is an example of the heavy metal oxide.

The average particle size of nanoparticles can be determined by cuttinga thin sample of hardened dental composition and measuring the particlediameter of about 50-100 particles using a transmission electronmicrograph at a magnification of 300,000 and calculating the average.

As used herein, “discrete” means unaggregated, individual particles(e.g. nanoparticles) that are separate from each other.

As used herein, a “nanocluster” generally refers to a group of two ormore nanoparticles associated by relatively weak, but sufficientintermolecular forces that cause the nanoparticles to clump to together,even when dispersed in a hardenable resin. Preferred nanoclusters cancomprise loosely aggregated substantially amorphous cluster of discretenon-fumed non-heavy metal oxide nanoparticles (e.g., silicananoparticles) and heavy metal oxide (e.g., zirconia). Where zirconia ispresent as the heavy metal oxide, the zirconia can be crystalline oramorphous. Furthermore, the heavy metal oxide can be present asparticles (e.g., discrete non-fumed heavy metal oxide nanoparticles suchas zirconia nanoparticles). The particles from which the nanocluster isformed preferably have an average diameter of 5 nm to about 100 nm.However, the average particle size of the loosely aggregated nanoclusteris typically considerably larger. Typically, the nanoclusters have alongest dimension in the micrometer range (e.g., 3 micrometers, 5micrometers, 7 micrometers, 10 micrometers, and in some cases, 30 to 50micrometers). Nanocluster size may be determined according to themethods generally described in U.S. Pat. No. 6,730,156 (column 21, lines1-22, “Cluster Size Determination”).

By “substantially amorphous” it is meant that the nanoclusters areessentially free of crystalline structure. Absence of crystallinity (orpresence of amorphous phases) is preferably determined by a procedurethat provides a Crystallinity Index, as generally described in U.S. Pat.No. 6,730,156 (column 21, lines 23 to column 22, line 33, “CrystallinityIndex Procedure”). The Crystallinity Index characterizes the extent amaterial is crystalline or amorphous, whereby a value of 1.0 isindicative of a fully crystalline structure, and a value near zeroindicates presence of amorphous phase only. The nanoclusters of thepresent disclosure preferably have an index of less than about 0.1; morepreferably less than about 0.05.

By “nano” is meant a material in a form having at least one dimensionthat is, on average, at most 200 nanometers (e.g., discrete non-fumedmetal oxide nanoparticles). Thus, nano materials refer to materialsincluding, for example, nanoparticles and nanoclusters, as definedherein. So, for example, “nanoparticles” refers to particles having anumber average diameter of at most 200 nanometers. As used herein for aspherical particle, “size” refers to the diameter of the particle. Asused herein for a non-spherical particle, “size” refers to the longestdimension of the particle. In certain embodiments, the nanoparticles arecomprised of discrete, non-aggregated and non-agglomerated particles.

As used herein, the term “ethylenically unsaturated compound” is meantto include monomers, oligomers, and polymers having at least oneethylenic unsaturation.

By “polymerization” is meant the forming of a higher weight materialfrom monomers or oligomers. The polymerization reaction also can involvea cross-linking reaction.

As used herein, the term “(meth)acrylate” is a shorthand reference toacrylate, methacrylate, or combinations thereof, and “(meth)acrylic” isa shorthand reference to acrylic, methacrylic, or combinations thereof.As used herein, “(meth)acrylate-functional compounds” are compounds thatinclude, among other things, a (meth)acrylate moiety.

As used herein a “hardened composite material” is the composite materialof the present disclosure that has undergone a physical and/or achemical transformation to produce a solid and firm composite materialthat is resistant to pressure. The physical and/or chemicaltransformation of the composite material can be due to a setting,curing, polymerizing, crosslinking or a fusing process.

As used herein “translucency” is the degree to which a materialtransmits light. This may be quantified by contrast ratio, translucencyparameter, or percent transmittance through a known thickness ofmaterial. Translucency in dental restorative materials is oftendetermined from the contrast ratio. The contrast ratio is the ratio ofwhite light remission from a specimen placed over a standardized blackbackground (R_(b)) and a standardized white background (R_(w)). Thecontrast ratio is calculated as CR=R_(b)/R_(w)×100. A contrast ratio of100 represents a completely opaque specimen. Translucency is expressedas 100-CR.

As used herein a “dental mill blank” is a block of material (e.g.,hardened composite material) from which dental product can be milled.

By “machining” is meant milling, grinding, cutting, carving, or shapinga material having a three dimensional structure or shape by a machine.

The term “comprising” and variations thereof (e.g., comprises, includes,etc.) do not have a limiting meaning where these terms appear in thedescription and claims.

As used herein, “CAD/CAM” is the abbreviation for computer-aideddesign/computer-aided manufacturing.

In the present disclosure, weight percentage (wt. %) values of thevarious components (e.g., at least a polymerizable component, ceramicfibers and nanoclusters) that make up the composite material arerecited. These wt. % values of the composite material are based on atotal weight of the composite material and the wt. % values of all thecomponents that are used to form the composite material of the presentdisclosure always total to a value of 100 wt. %.

The recitation herein of numerical ranges by endpoints is intended toinclude all numbers subsumed within that range (e.g. 1 to 5 includes 1,1.5, 2, 2.75, 3, 3.80, 4, and 5).

As used herein, “a” or “an” means “at least one” or “one or more” unlessotherwise indicated. In addition, the singular forms “a”, “an”, and“the” include plural referents unless the content clearly dictatesotherwise. Thus, for example, reference to a composition containing “acompound” includes a mixture of two or more compounds. As used in thisspecification and the appended claims, the term “or” is generallyemployed in its sense including “and/or” unless the content clearlydictates otherwise.

Unless otherwise indicated, all numbers expressing quantities ofingredients, measurement of properties such as contrast ratio and soforth used in the specification and claims can be modified in allinstances by the term “about.” Accordingly, unless indicated to thecontrary, the numerical parameters set forth in the foregoingspecification and attached claims are approximations that can varydepending upon the desired properties sought to be obtained by thoseskilled in the art utilizing the teachings of the present disclosure. Atthe very least, and not as an attempt to limit the application of thedoctrine of equivalents to the scope of the claims, each numericalparameter should at least be construed in light of the number ofreported significant digits and by applying ordinary roundingtechniques. Notwithstanding that the numerical ranges and parameterssetting forth the broad scope of the disclosure are approximations, thenumerical values set forth in the specific examples are reported asprecisely as possible. Any numerical value, however, inherently containscertain errors necessarily resulting from the standard deviations foundin their respective testing measurements.

As discussed herein, the composite material of the present disclosureincludes 4 to 50 weight percent (wt. %) of ceramic fibers, where the wt.% is based on a total weight of the composite material. Ceramic fibershaving weight percent's within this range are also possible. Forexample, the ceramic fibers of the composite material can have weightpercent's with a low value of any one of 4, 5, 6, 8, 10, 12, 16 or 18 toa high value of a given range of 50, 48, 45, 42, 40, 38, 36, 34, 32, 30,28, 24 or 20. Different combinations of the low value and the high valueare possible for the wt. % of ceramic fibers. Examples of suchcombinations include 4 to 40 wt. % of ceramic fibers in the compositematerial; 8 to 40 wt. % of ceramic fibers in the composite material or16 to 40 wt. % of ceramic fibers in the composite material, where thewt. % is based on a total weight of the composite material. Anycombination of the low value and the high value recited herein can beused to provide a range for the wt. % of ceramic fibers in the compositematerial.

The ceramic fibers of the composite material also each have a length. Aseach of the ceramic fibers can have a different length, the lengths ofthe ceramic fibers can be grouped into percentages of a total number ofthe ceramic fibers that are either above or below a given length value.For example, the ceramic fiber length “L” is giving by the fraction ofthe ceramic fibers that are either shorter or longer than a given value.These “L” values include a numerical prefix (e.g., “L10”, “L25”, “L50”,“L75”, “L90” or “L99”) that indicates the percentage (based on a totalnumber of the ceramic fibers) of the ceramic fibers that have a lengththat is either less than or equal to a given length value. So, forexample, “L10” can denote that 10% of the ceramic fibers are less thanor equal to the L10 length value, L50 can denote that 50% of the ceramicfibers are less than or equal to the L50 length value and 50% of theceramic fibers are greater than the L50 length value (this is also knownas the median length) and L90 can denote that 90% of the ceramic fibersare less than or equal to the L90 length value.

For the present disclosure, the length of fifty percent of the ceramicfibers (i.e., the “L50”), based on a total number of the ceramic fibers,is at least 50 micrometers and the length of ninety percent (%) of theceramic fibers (i.e., the “L90”), based on the total number of theceramic fibers, is no greater than 500 micrometers. In other words, forthe composite material of the present disclosure at least 50% of theceramic fibers (“L50”) have a length that is at least 50 micrometers andat least 90% of the ceramic fibers have a length that is no greater than500 micrometers. Other values and ranges are possible for the “L” valuesof the ceramic fibers that either fall below or above a given percentageof the total number of ceramic fibers. For example, the length ofsixty-five percent of the ceramic fibers (“L65”), based on a totalnumber of the ceramic fibers, can be at least 100 micrometers and thelength of ninety percent of the ceramic fibers (“L90”), based on thetotal number of the ceramic fibers, can be no greater than 350micrometers. The L90 values (length of ninety % of the ceramic fibersbased on the total number of the ceramic fibers) can also include anyone of the following values: less than equal to 475 micrometers; lessthan equal to 450 micrometers; less than equal to 425 micrometers; lessthan equal to 400 micrometers; less than equal to 375 micrometers; lessthan equal to 350 micrometers; less than equal to 325 micrometers; lessthan equal to 300 micrometers; less than equal to 275 or less than equalto 250 micrometers, while the L50 values (length of fifty % of theceramic fibers based on a total number of the ceramic fibers) can alsoinclude any one of the following values: at least 75 micrometers; atleast 100 micrometers; at least 125 micrometers; at least 150micrometers; at least 175 micrometers; at least 200 micrometers or atleast 225 micrometers, where combinations of ranges for the L90 and L50values are possible. Examples of such ranges for the L90 and L50 valuesinclude, but are not limited to, ceramic fibers of the presentdisclosure having an L90 value of less than equal to 475 micrometers andan L50 value of at least 75 micrometers; an L90 value of less than equalto 475 micrometers and an L50 value of at least 100 micrometers; and anL90 value of less than equal to 475 micrometers and an L50 value of atleast 100 micrometers.

The ceramic fibers of the present disclosure can also have an arithmeticmean length. For example, the ceramic fibers of the composite materialcan an arithmetic mean length of 50 micrometers to less than 500micrometers. Preferably, the ceramic fibers of the composite materialcan an arithmetic mean length of 100 micrometers to 170 micrometers. Theceramic fibers can also have an arithmetic mean diameter of 0.5 to 20micrometers. In one embodiment, the arithmetic mean diameter of theceramic fibers can be 6 to 15 micrometers. Preferably, the arithmeticmean diameter of the ceramic fibers is 8 to 13 micrometers. Mostpreferably, the arithmetic mean diameter of the ceramic fibers is 9 to12 micrometers. It is appreciated that in addition to a circularcross-section for the ceramic fibers, it is also possible to havedifferent cross-sectional shapes. Examples include, but are not limitedto, ribbon like, oval (non-circular) and polygonal (e.g., triangular orsquare), among others known in the art.

The size and shape of the ceramic fibers of the composite material canfurther be described based on their aspect ratio (e.g.,length-to-diameter ratio). It is appreciated that the cross-sectionalshape of the ceramic fiber may not be exactly circular. As such, thecross-sectional area of the ceramic fiber can be used to arrive at a“diameter” value to be used for the aspect ratio discussed herein. Forthe present disclosure an aspect ratio of a median length of the fiftypercent of the ceramic fibers that have a length of at least 50micrometers to a median diameter of the fifty percent of the ceramicfibers that have a length of at least 50 micrometers is at least 5:1(median length : median diameter).

The ceramic fibers of the present disclosure can have a variety ofcompositions. Preferably, the ceramic fibers of the present disclosureare at least partially amorphous ceramic fibers. More preferably, theceramic fibers of the present disclosure are completely amorphousceramic fibers. The ceramic fibers can be produced in continuouslengths, which are chopped or sheared, as discussed herein, to providethe ceramic fibers of the present disclosure.

The ceramic fibers of the present disclosure can be produced from avariety of commercially available ceramic filaments. Examples offilaments useful in forming the ceramic fibers of the present disclosureinclude the ceramic oxide fibers sold under the Trademark Nextel™ (3MCompany, St. Paul, Minn.). Nextel™ is a continuous filament ceramicoxide fiber having low elongation and shrinkage at operatingtemperatures, and offer good chemical resistance, low thermalconductivity, thermal shock resistance and low porosity. Specificexamples of Nextel™ include Nextel™ 312, Nextel™ 440, Nextel™ 550,Nextel™ 610 and Nextel™ 720. Nextel™ 312 and Nextel™ 440 are refractoryaluminoborosilicate that includes Al₂O₃, SiO₂ and B₂O₃. Nextel™ 550 andNextel™ 720 are aluminosilica and Nextel™ 610 is alumina.

Certain of the Nextel™ ceramic oxide fibers are preferred due to thepresence of aluminoborosilicate, which provides for desirable refractiveindex values and the ability of the composite material to polish to adesired gloss, as presented in the Examples herein. Preferably, theceramic fibers are formed from Nextel™ 312. Nextel™ 312 has a chemicalcomposition, in weight percent (wt. %), of 62.5 wt. %, Al₂O₃, 24.5 wt. %SiO₂ and 13 wt. % boron trioxide (B₂O₃), where the wt. % are based onthe total weight of the ceramic fiber. Nextel™ 312 has a filamentdiameter of 10 to 12 micrometers, a Refractive Index of 1.568 and asurface area (m²/g), as provided from 3M, of less than 0.2. Nextel™ 440has a chemical composition of 70 wt. %, Al₂O₃, 28 wt. % SiO₂ and 2 wt. %B₂O₃, a filament diameter of 10 to 12 micrometers, a Refractive Index of1.614 and a surface area (m²/g), as provided from 3M, of less than 0.2.Nextel™ 550 has a chemical composition of 73 wt. %, Al₂O₃ and 27 wt. %SiO₂, a filament diameter of 10 to 12 micrometers, a Refractive Index of1.602 and a surface area (m²/g), as provided from 3M, of less than 0.2.

During manufacture, the NEXTEL™ filaments are coated with organicsizings or finishes which serves as aids in textile processing. Sizingcan include the use of starch, oil, wax or other organic ingredientsapplied to the filament strand to protect and aid handling. Sizings canalso include a surface treatment, such as with a silane, where thesurface treatment may or may not include polymerizable groups. Thesizing can be removed from the ceramic filaments by heat treating thefilaments or ceramic fibers as a temperature of 700° C. for one to fourhours.

Ceramic fibers according to the present disclosure can also be formedfrom other suitable ceramic oxide filaments. Examples of such ceramicoxide filaments include those available from Central Glass Fiber Co.,Ltd. (e.g., EFH75-01, EFH150-31). Also preferred are aluminoborosilicateglass fibers which are which contain less than about 2% alkali or aresubstantially free of alkali (i.e., “E-glass” fibers). E-glass fibersare available from numerous commercial suppliers.

As discussed herein, the ceramic fibers of the present disclosure can becut or chopped so as to provide the percentage of fibers lengths in theranges discussed herein. Producing ceramic fibers having this range ofrelatively uniform lengths can be accomplished by cutting continuousfilaments of the ceramic material in a mechanical shearing operation orlaser cutting operation, among other cutting operations. Given thehighly controlled nature of such cutting operations, the sizedistribution of the ceramic fibers is very narrow, thereby allowing forthe length of fifty percent of the ceramic fibers (i.e., the “L50”),based on a total number of the ceramic fibers, to be at least 50micrometers and the length of ninety percent of the ceramic fibers(i.e., the “L90”), based on the total number of the ceramic fibers, tobe no greater than 500 micrometers.

It has been observed that there is a direct correlation betweenimprovements in the handling of the composite material and the narrowsize distribution of the ceramic fibers as discussed herein. So, forexample, as the size distribution of the ceramic fibers is reduced thereis expected to be a significant improvement in the handling of thecomposite material, all other things being equal. This is a verydesirable feature of the present disclosure, especially for dentalrestorative material applications. In contrast to the ceramic fibers ofthe present disclosure, milled or ground versions of the ceramic fibersnot displaying such a narrow size distribution in the stated rangesproduce composite materials that are problematic. For example, if thenumber of ceramic fibers greater than 500 micrometers is too large theirpresence in the composite material produces poor handling properties,while if the number of ceramic fibers less than 50 micrometers is toolarge their presence in the composite material produces less thandesirable mechanical properties in the cured composite material.

The ceramic fibers of the present disclosure can also be treated inorder to modify their surface properties. For example, treating theceramic fibers with boiling water can help to removing sizing from theceramic fibers. Treating the ceramic fibers with boiling water can alsohelp to change the surface area of the ceramic fibers. So, for example,it has been found that etching the surface of boroaluminosilicate fibers(e.g., Nextel™ 312) through a boiling water method helps to leach borontrioxide from these fibers. The boiling water method can includedispersing the ceramic filament or ceramic fibers in deionized water andboiling the mixture for a predetermined time at atmospheric pressure.Predetermined times for boiling can depend upon the composition of anysizing used with the ceramic fiber and/or the composition of the ceramicfiber itself. Examples of suitable times for the predetermined times forthe boiling water method include, but are not limited to, 10 minutes(min.), 15 min., 20 min., 25 min., 30 min., 35 min., 40 min., 45 min.,50 min., 55 min., 60 min., 65 min., 70 min., 75 min., 80 min., 85 min.,90 min., 95 min., 100 min., 105 min., 110 min., 115 min. and 120 min.Other predetermined times are possible. In one embodiment, the Nextel™312 filament having undergone the boiling water method for 90 min. hadless than 14 weight percent of boron trioxide based on the total weightof the ceramic fibers.

Sizing and/or specific portions of the ceramic fiber could also beremoved through etching with an acid or a base. A heat treatment canalso be used to remove sizing from the ceramic fiber. It is alsopossible to remove any sizing and/or specific portions of the ceramicfiber through laser or plasma ablation.

In addition to removing components from the ceramic fibers, treating theceramic fibers to modify their surface properties also causes anincrease in the surface area of the ceramic fibers. For example, ceramicfibers of the present disclosure can be treated (e.g., with boilingwater for 90 min.) so as to increase their surface area to at least 10square meters per gram (m²/g). Measurements of the surface area of theceramic fibers as discussed herein can be accomplished using thetechnique developed by Brunauer, Emmett and Teller, see S. Brunauer,“Physical Adsorption” (Princeton University Press, Princeton, N.J.,1945), commonly referred to as “BET” gas adsorption.

The result is an increase in the surface area of these ceramic fibersand subsequently better coupling of these ceramic fibers into thepolymerizable component. Using such ceramic fibers helps the compositematerial of the present disclosure to retain good mechanical propertiessuch as flexural strength, which is an important property for dentalrestorative materials, as well as for good composite performance ingeneral applications. One or more (e.g., two or more) of a couplingagent can also be used with the ceramic fiber after they have beentreated to remove any sizing and/or to increase their surface area. Oneor more of the coupling agent can also be used with the fillerparticles, as discussed herein. So, combinations of two or more couplingagents, as discussed herein, can be used with the ceramic fiber andfiller particles, when present, in the composite material. In someembodiments, such coupling agents can help to provide a chemical bond(e.g., a covalent bond) between the polymerizable component and theceramic fibers and, when present, the filler particles. The couplingagent is a compound capable of reacting with both the polymerizablecomponent and the ceramic fibers and the filler particles (whenpresent), thereby acting as interface between the polymerizedpolymerizable component and the ceramic fibers and the filler particles(when present). The ceramic fibers and the filler particles (whenpresent) can be treated with the coupling agent prior to admixing withthe polymerizable component. Thus, in some embodiment, the couplingagent includes a polymerizable group, such as for example one or moreepoxy, acrylate and/or (meth)acrylate groups. In other embodiments, thecoupling agent does not include polymerizable group.

For the various embodiments, the coupling agent can be selected from thegroup consisting of an organosilane coupling agent, a titanate couplingagent, a zirconate coupling agent, an acidic coupling agent or acombination thereof. The coupling agent may be applied to the inorganicmaterials (e.g., the ceramic fibers and filler particles, when present)as a pre-treatment and/or added to the polymerizable component.

Organosilane coupling agents have the general formula R_(n)SiX_((4-n)).The functional group “X” is involved in the reaction with the substrate,where X is independently at each occurrence a hydrolyzable group such asan alkoxy, an acyloxy or an amine. R is a non-hydrolyzable organicradical that possesses a functionality that enables the organosilanecoupling agent to bond with, or improve compatibility with, organicpolymers and the like. Suitable examples of organosilane coupling agentsinclude gamma-methacryloxypropyltrimethoxysilane,gamma-methacryloxyoctyltrimethoxysilane,gamma-mercaptopropyltriethoxysilane, gamma-aminopropyltrimethoxysilane,beta-(3,4-epoxycyclohexyl)ethyltrimethoxysilane,gamma-glycidoxypropyltrimethoxysilane, and the like. Other suitableexamples of organosilane coupling agents includen-octyltrimethoxysilane, phenyltrimethoxysilane, and the like. Mixturesof organosilane coupling agents may be used.

Titanate coupling agents include a family of monoalkoxy titanates usefulin conjunction with the ceramic fibers and the filler particles, whenpresent. Titanate couplers typically have three pendant organicfunctional groups. The titanate couplers also act as plasticizers toenable much higher loadings and/or to achieve better flow. A suitableexample of a titanate coupling reagent includes methoxydiethyleneglycoltrimethacryloyl titanate.

Zirconate coupling agents include 2,2-di(allyloxymethyl)butyltrimethacryloyl zirconate.

Acidic coupling agents include mono-2-(methacryloyloxy)ethyl succinate.The composite material of the present disclosure is hardenable due thepresence of the polymerizable component. The composite material includes20 to 40 wt. % of the polymerizable component. In some embodiments, thecomposite material can be hardened (e.g., polymerized by conventionalphotopolymerization and/or chemical polymerization techniques) prior toapplying it to an oral surface. In other embodiments, the compositematerial can be hardened (e.g., polymerized by conventionalphotopolymerization and/or chemical polymerization techniques) after ithas been applied to an oral surface.

Examples of the polymerizable component include, but are not limited to,those having sufficient strength, hydrolytic stability, and non-toxicityto render them suitable for use in the oral environment. Examples ofsuch materials include acrylates, methacrylates, urethanes,carbamoylisocyanurates and epoxy resins (e.g., those shown in U.S. Pat.No. 3,066,112 (Bowen); U.S. Pat. No. 3,539,533 (Lee II et al.); U.S.Pat. No. 3,629,187 (Waller); U.S. Pat. No. 3,709,866 (Waller); U.S. Pat.No. 3,751,399 (Lee et al.); U.S. Pat. No. 3,766,132 (Lee et al.); U.S.Pat. No. 3,860,556 (Taylor); U.S. Pat. No. 4,002,669 (Gross et al.);U.S. Pat. No. 4,115,346 (Gross et al.); U.S. Pat. No. 4,259,117(Yamauchi et al.); U.S. Pat. No. 4,292,029 (Craig et al.); U.S. Pat. No.4,308,190 (Walkowiak et al.); U.S. Pat. No. 4,327,014 (Kawahara et al.);U.S. Pat. No. 4,379,695 (Orlowski et al.); U.S. Pat. No. 4,387,240(Berg); U.S. Pat. No. 4,404,150 (Tsunekawa et al.)); and mixtures andderivatives thereof.

In certain embodiments, the polymerizable component of the compositematerial is photopolymerizable, i.e., the polymerizable componentcontains a photoinitiator system that upon irradiation with actinicradiation initiates the polymerization (or hardening) of the compositematerial. In other embodiments, the polymerizable component of thecomposite material is chemically hardenable, i.e., the polymerizablecomponent contains a chemical initiator (i.e., initiator system) thatcan polymerize, cure, or otherwise harden the composite material withoutdependence on irradiation with actinic radiation. Such chemicallyhardenable compositions are sometimes referred to as “self-cure”compositions.

The polymerizable component typically includes one or more ethylenicallyunsaturated compounds with or without acid functionality. Examples ofuseful ethylenically unsaturated compounds include acrylic acid esters,methacrylic acid esters, hydroxy-functional acrylic acid esters,hydroxy-functional methacrylic acid esters, and combinations thereof.

The composite material, especially in photopolymerizableimplementations, may include compounds having free radically activefunctional groups that may include monomers, oligomers, and polymershaving one or more ethylenically unsaturated group. Suitable compoundscontain at least one ethylenically unsaturated bond and are capable ofundergoing addition polymerization. Such free radically polymerizablecompounds include mono-, di- or poly-(meth)acrylates (i.e., acrylatesand methacrylates) such as, methyl (meth)acrylate, ethyl acrylate,isopropyl methacrylate, n-hexyl acrylate, stearyl acrylate, allylacrylate, glycerol triacrylate, ethyleneglycol diacrylate,diethyleneglycol diacrylate, triethyleneglycol dimethacrylate,1,3-propanediol di(meth)acrylate, trimethylolpropane triacrylate,1,2,4-butanetriol trimethacrylate, 1,4-cyclohexanediol diacrylate,pentaerythritol tetra(meth)acrylate, sorbitol hexacrylate,tetrahydrofurfuryl (meth)acrylate,bis[1-(2-acryloxy)]-p-ethoxyphenyldimethylmethane,bis[1-(3-acryloxy-2-hydroxy)]-p-propoxyphenyldimethylmethane,ethoxylated bisphenol A di(meth)acrylate, and trishydroxyethyl-isocyanurate trimethacrylate; (meth)acrylamides (i.e.,acrylamides and methacrylamides) such as (meth)acrylamide, methylenebis-(meth)acrylamide, and diacetone (meth)acrylamide; urethane(meth)acrylates; the bis-(meth)acrylates of polyethylene glycols(preferably of molecular weight 200-500), copolymerizable mixtures ofacrylated monomers such as those in U.S. Pat. No. 4,652,274 (Boettcheret al.), acrylated oligomers such as those of U.S. Pat. No. 4,642,126(Zador et al.), and poly(ethylenically unsaturated) carbamoylisocyanurates such as those disclosed in U.S. Pat. No. 4,648,843(Mitra); and vinyl compounds such as styrene, diallyl phthalate, divinylsuccinate, divinyl adipate and divinyl phthalate. Other suitable freeradically polymerizable compounds include siloxane-functional(meth)acrylates as disclosed, for example, in WO-00/38619 (Guggenbergeret al.), WO-01/92271 (Weinmann et al.), WO-01/07444 (Guggenberger etal.), WO-00/42092 (Guggenberger et al.) and fluoropolymer-functional(meth)acrylates as disclosed, for example, in U.S. Pat. No. 5,076,844(Fock et al.), U.S. Pat. No. 4,356,296 (Griffith et al.), EP-0373 384(Wagenknecht et al.), EP-0201 031 (Reiners et al.), and EP-0201 778(Reiners et al.). Mixtures of two or more free radically polymerizablecompounds can be used if desired. In some embodiments, amethacryloyl-containing compound may be utilized.

The polymerizable component may also contain hydroxyl groups andethylenically unsaturated groups in a single molecule. Examples of suchmaterials include hydroxyalkyl (meth)acrylates, such as 2-hydroxyethyl(meth)acrylate and 2-hydroxypropyl (meth)acrylate; glycerol mono- ordi-(meth)acrylate; trimethylolpropane mono- or di-(meth)acrylate;pentaerythritol mono-, di-, and tri-(meth)acrylate; sorbitol mono-, di-,tri-, tetra-, or penta-(meth)acrylate; and2,2-bis[4-(2-hydroxy-3-methacryloxypropoxy)phenyl]propane (bisGMA).Suitable ethylenically unsaturated compounds are also available from awide variety of commercial sources, such as Sigma-Aldrich, St. Louis.Mixtures of ethylenically unsaturated compounds can be used if desired.

In certain embodiments, the polymerizable component includes a compoundselected from the group consisting of dimethacrylates of polyethyleneglycols of 200 to 1000 weight average molecular weight, such as PEGDMA(polyethyleneglycol dimethacrylate having a molecular weight ofapproximately 400), bisGMA, UDMA (urethane dimethacrylate), GDMA(glycerol dimethacrylate), TEGDMA (triethyleneglycol dimethacrylate), 2to 10 mole ethoxylated Bisphenol-A dimethacrylate (Bis-EMA), such asbisEMA6 as described in U.S. Pat. No. 6,030,606 (Holmes), NPGDMA(neopentylglycol dimethacrylate), glycerol dimethacrylate,1,3-propanediol dimethacrylate and 2-hydroxethyl methacrylate. Variouscombinations of these hardenable components can be used. For certainembodiments, including any one of the above embodiments, thepolymerizable resin comprises a compound selected from the groupconsisting of2,2-bis[4-(2-hydroxy-3-methacryloyloxypropoxy)phenyl]propane (bisGMA),triethyleneglycol dimethacrylate (TEGDMA), urethane dimethacrylate(UDMA), 2 to 10 mole ethoxylated Bisphenol-A dimethacrylate (bisEMA),dimethacrylates of polyethylene glycols of 200 to 1000 weight averagemolecular weight, glycerol dimethacrylate, 1,3-propanedioldimethacrylate, and a combination thereof.

When the composite material contains an ethylenically unsaturatedcompound without acid functionality, it is generally present in anamount of at least 5% by weight, more typically at least 10% by weight,and most typically at least 15% by weight ethylenically unsaturatedcompounds without acid functionality, based on the total weight of theunfilled composition. The compositions of the present disclosuretypically include at most 95% by weight, more typically at most 90% byweight, and most typically at most 80% by weight ethylenicallyunsaturated compounds without acid functionality, based on the totalweight of the unfilled composition.

In some embodiments, the polymerizable component may include one or moreethylenically unsaturated compounds with acid functionality. As usedherein, ethylenically unsaturated compounds “with acid functionality” ismeant to include monomers, oligomers, and polymers having ethylenicunsaturation and acid and/or acid-precursor functionality.Acid-precursor functionalities include, for example, anhydrides, acidhalides, and pyrophosphates. The acid functionality can includecarboxylic acid functionality, phosphoric acid functionality, phosphonicacid functionality, sulfonic acid functionality, or combinationsthereof.

Ethylenically unsaturated compounds with acid functionality include, forexample, a, ß-unsaturated acidic compounds such as glycerol phosphatemono(meth)acrylates, glycerol phosphate di(meth)acrylates, hydroxyethyl(meth)acrylate (e.g., HEMA) phosphates, bis((meth)acryloxyethyl)phosphate, ((meth)acryloxypropyl) phosphate, bis((meth)acryloxypropyl)phosphate, bis((meth)acryloxy)propyloxy phosphate, (meth)acryloxyhexylphosphate, bis((meth)acryloxyhexyl) phosphate, (meth)acryloxyoctylphosphate, bis((meth)acryloxyoctyl) phosphate, (meth)acryloxydecylphosphate, bis((meth)acryloxydecyl) phosphate, caprolactone methacrylatephosphate, citric acid di- or tri-methacrylates, poly(meth)acrylatedoligomaleic acid, poly(meth)acrylated polymaleic acid,poly(meth)acrylated poly(meth)acrylic acid, poly(meth)acrylatedpolycarboxyl-polyphosphonic acid, poly(meth)acrylatedpolychlorophosphoric acid, poly(meth)acrylated polysulfonate,poly(meth)acrylated polyboric acid, and the like, may be used ascomponents in the hardenable component system. Also monomers, oligomers,and polymers of unsaturated carbonic acids such as (meth)acrylic acids,aromatic (meth)acrylated acids (e.g., methacrylated trimellitic acids),and anhydrides thereof can be used. Certain preferred compositions ofthe present disclosure include an ethylenically unsaturated compoundwith acid functionality having at least one P—OH moiety.

When the composition contains an ethylenically unsaturated compound withacid functionality, it is generally present in an amount of at least 1%by weight, more typically at least 3% by weight, and most typically atleast 5% by weight ethylenically unsaturated compounds with acidfunctionality, based on the total weight of the unfilled composition.The compositions of the present disclosure typically include at most 80%by weight, more typically at most 70% by weight, and most typically atmost 60% by weight ethylenically unsaturated compounds with acidfunctionality, based on the total weight of the unfilled composition.

For free radical polymerization (hardening), an initiation system can beselected from systems which initiate polymerization via radiation, heat,or redox/auto-cure chemical reaction. A class of initiators capable ofinitiating polymerization of free radically active functional groupsincludes free radical-generating photoinitiators, optionally combinedwith a photosensitizer or accelerator. Such initiators typically can becapable of generating free radicals for addition polymerization uponexposure to light energy having a wavelength between 200 and 800 nm.

In certain embodiments, one or more thermally activated initiators areused to enable thermal hardening of the polymerizable component.Examples of thermal initiators include peroxides and azo compounds suchas benzoyl peroxide, lauryl peroxide, 2,2-azobis-isobutyronitrile(AIBN).

In certain embodiments, the thermally activated initiator is chosen suchthat appreciable amounts of free-radical initiating species are notproduced at temperatures below about 100° C. “Appreciable amounts”refers an amount sufficient to cause polymerization and/or crosslinkingto the extent that a noticeable change in properties (e.g., viscosity,moldability, hardness, etc.) of the composite material occurs. Forcertain embodiments, the initiator is activated within the temperaturerange of 120 to 140° C., or, in some embodiments, 130 to 135° C. Forcertain of these embodiments, the initiator is an organic peroxide whichcan be thermally activated to produce appreciable amounts offree-radical initiating species within any of these temperature ranges.For certain of these embodiments, the initiator is selected from thegroup consisting of dicumyl peroxide, t-butyl peroxide, and acombination thereof. For certain of these embodiments, the initiator isdicumyl peroxide. In other embodiments, the initiator is selected from2,5-bis(tert-butylperoxy)-2,5-dimethylhexane;2,5-bis(tert-butylperoxy)-2,5-dimethyl-3-hexyne;bis(1-(tert-butylperoxy)-1-methylethy)benzene; tert-butyl peracetate;tert-butyl peroxybenzoate; cumene hydroperoxide; 2,4-pentanedioneperoxide; peracetic acid, and combinations thereof.

For certain embodiments, the thermally activated initiator is present inthe composition in an amount of at least 0.2 percent based upon theweight of the polymerizable component. For certain of these embodiments,the initiator is present in an amount of at least 0.5 percent. Forcertain of these embodiments, the initiator is present in thecomposition in the amount of not more than 3 percent based upon theweight of the polymerizable component. For certain of these embodiments,the initiator is present in an amount of not more than 2 percent.

In certain embodiments, the composition may additionally bephotopolymerizable, i.e., the composition contains a photoinitiatorsystem that upon irradiation with actinic radiation initiatespolymerization (curing or hardening) of the composition. Suitablephotoinitiators (i.e., photoinitiator systems that include one or morecompounds) for polymerizing free radically photopolymerizablecompositions include binary and tertiary systems. Typical tertiaryphotoinitiators include an iodonium salt, a photosensitizer, and anelectron donor compound as described in U.S. Pat. No. 5,545,676(Palazzotto et al.). Suitable iodonium salts are the diaryl iodoniumsalts, e.g., diphenyliodonium chloride, diphenyliodoniumhexafluorophosphate, diphenyliodonium tetrafluoroborate, andtolylcumyliodonium tetrakis(pentafluorophenyl)borate. Suitablephotosensitizers are monoketones and diketones that absorb some lightwithin a range of 400 nm to 520 nm (preferably, 450 nm to 500 nm).Particularly suitable compounds include alpha diketones that have lightabsorption within a range of 400 nm to 520 nm (even more preferably, 450to 500 nm). Suitable compounds are camphorquinone, benzil, furil,3,3,6,6-tetramethylcyclohexanedione, phenanthraquinone,1-phenyl-1,2-propanedione and other 1-aryl-2-alkyl-1,2-ethanediones, andcyclic alpha diketones. Suitable electron donor compounds includesubstituted amines, e.g., ethyl dimethylaminobenzoate. Other suitabletertiary photoinitiator systems useful for photopolymerizingcationically polymerizable resins are described, for example, in U.S.Pat. No. 6,765,036 (Dede et al.).

Other useful photoinitiators for polymerizing free radicallyphotopolymerizable compositions include the class of phosphine oxidesthat typically have a functional wavelength range of 380 nm to 1200 nm.Preferred phosphine oxide free radical initiators with a functionalwavelength range of 380 nm to 450 nm are acyl and bisacyl phosphineoxides such as those described in U.S. Pat. No. 4,298,738 (Lechtken etal.), U.S. Pat. No. 4,324,744 (Lechtken et al.), U.S. Pat. No. 4,385,109(Lechtken et al.), U.S. Pat. No. 4,710,523 (Lechtken et al.), and U.S.Pat. No. 4,737,593 (Ellrich et al.), U.S. Pat. No. 6,251,963 (Kohler etal.); and EP Application No. 0 173 567 A2 (Ying).

Commercially available phosphine oxide photoinitiators capable offree-radical initiation when irradiated at wavelength ranges ofdifferent from 380 nm to 450 nm includebis(2,4,6-trimethylbenzoyl)phenyl phosphine oxide (IRGACURE 819, CibaSpecialty Chemicals, Tarrytown, N.Y.),bis(2,6-dimethoxybenzoyl)-(2,4,4-trimethylpentyl) phosphine oxide (CGI403, Ciba Specialty Chemicals), a 25:75 mixture, by weight, ofbis(2,6-dimethoxybenzoyl)-2,4,4-trimethylpentyl phosphine oxide and2-hydroxy-2-methyl-1-phenylpropan-1-one (IRGACURE 1700, Ciba SpecialtyChemicals), a 1:1 mixture, by weight, ofbis(2,4,6-trimethylbenzoyl)phenyl phosphine oxide and2-hydroxy-2-methyl-1-phenylpropane-1-one (DAROCUR 4265, Ciba SpecialtyChemicals), and ethyl 2,4,6-trimethylbenzylphenyl phosphinate (LUCIRINLR8893X, BASF Corp., Charlotte, N.C.).

The phosphine oxide initiator may be used in the photopolymerizablecomposition in catalytically effective amounts, such as from 0.1 weightpercent to 5.0 weight percent, based on the total weight of the unfilledcomposition.

Tertiary amine reducing agents may be used in combination with anacylphosphine oxide. Illustrative tertiary amines useful in thedisclosure include ethyl 4-(N,N-dimethylamino)benzoate andN,N-dimethylaminoethyl methacrylate. When present, the amine reducingagent is present in the photopolymerizable composition in an amount from0.1 weight percent to 5.0 weight percent, based on the total weight ofthe unfilled composition. Useful amounts of other initiators are wellknown to those of skill in the art.

Polymerizable components made from cationically curable materialsuitable for use in the present disclosure can also include epoxyresins. Epoxy resins impart high toughness to composites, a desirablefeature, for example, dental mill blanks. Epoxy resins may optionally beblended with various combinations of polyols, methacrylates, acrylates,or vinyl ethers. Preferred epoxy resins include diglycidyl ether ofbisphenol A (e.g. EPON 828, EPON 825; Shell Chemical Co.),3,4-epoxycyclohexylmethyl-3-4-epoxy cyclohexene carboxylate (e.g.UVR-6105, Union Carbide), bisphenol F epoxides (e.g. GY-281;Ciba-Geigy), and polytetrahydrofuran.

As used herein, “cationically active functional groups” is a chemicalmoiety that is activated in the presence of an initiator capable ofinitiating cationic polymerization such that it is available forreaction with other compounds bearing cationically active functionalgroups. Materials having cationically active functional groups includecationically polymerizable epoxy resins. Such materials are organiccompounds having an oxirane ring, i.e., a group which is polymerizableby ring opening. These materials include monomeric epoxy compounds andepoxides of the polymeric type and can be aliphatic, cycloaliphatic,aromatic or heterocyclic. These materials generally have, on theaverage, at least 1 polymerizable epoxy group per molecule, preferablyat least about 1.5 and more preferably at least about 2 polymerizableepoxy groups per molecule. The polymeric epoxides include linearpolymers having terminal epoxy groups (e.g., a diglycidyl ether of apolyoxyalkylene glycol), polymers having skeletal oxirane units (e.g.,polybutadiene polyepoxide), and polymers having pendent epoxy groups(e.g., a glycidyl methacrylate polymer or copolymer). The epoxides maybe pure compounds or may be mixtures of compounds containing one, two,or more epoxy groups per molecule. The “average” number of epoxy groupsper molecule is determined by dividing the total number of epoxy groupsin the epoxy-containing material by the total number of epoxy-containingmolecules present.

These epoxy-containing materials may vary from low molecular weightmonomeric materials to high molecular weight polymers and may varygreatly in the nature of their backbone and substituent groups.Illustrative of permissible substituent groups include halogens, estergroups, ethers, sulfonate groups, siloxane groups, nitro groups,phosphate groups, and the like. The weight average molecular weight ofthe epoxy-containing materials may vary from about 58 to about 100,000or more. Molecular weights (e.g., weight average molecular weights) forthe present disclosure are measured using size exclusion chromatographywith polystyrene standards.

Useful epoxy-containing materials include those which containcyclohexane oxide groups such as epoxycyclohexanecarboxylates, typifiedby 3,4-epoxycyclohexylmethyl-3,4-epoxycyclohexanecarboxylate,3,4-epoxy-2-methylcyclohexylmethyl-3,4-epoxy-2-methylcyclohexanecarboxylate, and bis(3,4-epoxy-6-methylcyclohexylmethyl) adipate. For amore detailed list of useful epoxides of this nature, reference is madeto the U.S. Pat. No. 3,117,099, which is incorporated herein byreference.

Blends of various epoxy-containing materials are also contemplated.Examples of such blends include two or more weight average molecularweight distributions of epoxy-containing compounds, such as lowmolecular weight (below 200), intermediate molecular weight (about 200to 10,000) and higher molecular weight (above about 10,000).Alternatively or additionally, the epoxy resin may contain a blend ofepoxy-containing materials having different chemical natures, such asaliphatic and aromatic, or functionalities, such as polar and non-polar.Other types of useful materials having cationically active functionalgroups include vinyl ethers, oxetanes, spiro-orthocarbonates,spiro-orthoesters, and the like.

For hardening polymerizable components comprising cationically activefunctional groups, an initiation system can be selected from systemswhich initiate polymerization via radiation, heat, or redox/auto-curechemical reaction. For example, epoxy polymerization may be accomplishedby the use of thermal curing agents, such as anhydrides or amines. Aparticularly useful example of an anhydride curing agent would becis-1,2-cyclohexanedicarboxylic anhydride.

Alternatively, initiation systems for polymerizable componentscomprising cationically active functional groups are those that arephotoactivated. The broad class of cationic photoactive groupsrecognized in the catalyst and photoinitiator industries may be used inthe practice of the present disclosure. Photoactive cationic nuclei,photoactive cationic moieties, and photoactive cationic organiccompounds are art recognized classes of materials as exemplified by U.S.Pat. Nos. 4,250,311; 3,708,296; 4,069,055; 4,216,288; 5,084,586;5,124,417; 4,985,340, 5,089,536, and 5,856,373, each of which isincorporated herein by reference.

The cationically-curable materials can be combined with a threecomponent or ternary photoinitiator system, as described above. Threecomponent initiator systems are also described in U.S. Pat. Nos.6,025,406 and 5,998,549, each of which is incorporated herein byreference.

The chemically hardenable compositions may include redox cure systemsthat include a polymerizable component (e.g., an ethylenicallyunsaturated polymerizable component) and redox agents that include anoxidizing agent and a reducing agent. The reducing and oxidizing agentsshould react with or otherwise cooperate with one another to producefree-radicals capable of initiating polymerization of the polymerizablecomponent (e.g., the ethylenically unsaturated component). This type ofcure is a dark reaction, that is, it is not dependent on the presence oflight and can proceed in the absence of light. The reducing andoxidizing agents are preferably sufficiently shelf-stable and free ofundesirable colorization to permit their storage and use under typicaldental conditions.

Useful reducing agents include ascorbic acid, ascorbic acid derivatives,and metal complexed ascorbic acid compounds; amines, especially tertiaryamines, such as 4-tert-butyl dimethylaniline; aromatic sulfinic salts,such as p-toluenesulfinic salts and benzenesulfinic salts; thioureas,such as 1-ethyl-2-thiourea, tetraethyl thiourea, tetramethyl thiourea,1,1-dibutyl thiourea, and 1,3-dibutyl thiourea; and mixtures thereof.Other secondary reducing agents may include cobalt (II) chloride,ferrous chloride, ferrous sulfate, hydrazine, hydroxylamine (dependingon the choice of oxidizing agent), salts of a dithionite or sulfiteanion, and mixtures thereof. Preferably, the reducing agent is an amine.

Suitable oxidizing agents will also be familiar to those skilled in theart, and include but are not limited to persulfuric acid and saltsthereof, such as sodium, potassium, ammonium, cesium, and alkyl ammoniumsalts. Additional oxidizing agents include peroxides such as benzoylperoxides, hydroperoxides such as cumyl hydroperoxide, t-butylhydroperoxide, and amyl hydroperoxide, as well as salts of transitionmetals such as cobalt (III) chloride and ferric chloride, cerium (IV)sulfate, perboric acid and salts thereof, permanganic acid and saltsthereof, perphosphoric acid and salts thereof, and mixtures thereof.

It may be desirable to use more than one oxidizing agent or more thanone reducing agent. Small quantities of transition metal compounds mayalso be added to accelerate the rate of redox cure.

The reducing and oxidizing agents are present in amounts sufficient topermit an adequate free-radical reaction rate. This can be evaluated bycombining all of the ingredients of the composition except for theoptional filler, and observing whether or not a hardened mass isobtained.

Typically, the reducing agent, if used at all, is present in an amountof at least 0.01% by weight, and more typically at least 0.1% by weight,based on the total weight (including water) of the components of thecomposition. Typically, the reducing agent is present in an amount of nogreater than 10% by weight, and more typically no greater than 5% byweight, based on the total weight (including water) of the components ofthe composition.

Typically, the oxidizing agent, if used at all, is present in an amountof at least 0.01% by weight, and more typically at least 0.10% byweight, based on the total weight (including water) of the components ofthe composition. Typically, the oxidizing agent is present in an amountof no greater than 10% by weight, and more typically no greater than 5%by weight, based on the total weight (including water) of the componentsof the composition.

When used as a dental restorative material, the composite material canhave a variety of weight percent values for the ceramic fibers and/orthe nanoclusters depending upon the dental application. So, for example,if used as a sealant, the composite material of the disclosure can befilled with the ceramic fibers and/or the nanoclusters so as to providea flowable composite. In such implementations, the viscosity of thecomposite material is sufficiently low to allow its penetration intopits and fissures of occlusal tooth surfaces as well as into etchedareas of enamel, thereby aiding in the retention of the compositematerial. In applications where high strength or durability are desired(e.g., anterior or posterior restoratives, prostheses, crown and bridgecements, artificial crowns, artificial teeth and dentures) the loadinglevel of the ceramic fibers and the nanoclusters can be tailored so asto provide a more rigid composite.

The composite material further includes 20 to 70 wt. % of nanoclusters.The composite material can also include other value ranges for thenanoclusters. For example, the composite material can also include forthe wt. % of the nanoclusters lower limit values of: 20, 22, 25, 30, 35or 40, and upper limit values of 70, 65, 64, 60, 55, 50 or 45. Thisallows for a variety of possible ranges for the wt. % of thenanoclusters in the composite material. Examples of such ranges include,but are not limited to, 25 to 70 wt. % of nanoclusters, 25 to 65 wt. %of nanoclusters, 25 to 60 wt. % of nanoclusters, 25 to 55 wt. % ofnanoclusters, where a range of 22 to 64 wt. % of nanoclusters ispreferred.

As discussed herein, for a given combination of components that formsthe composite material the wt. % of each of the components adds to 100wt. % (wt. % based on the total weight of the composite material).Preferably, the nanoclusters are silica-zirconia nanoclusters formedfrom silica nanoparticles and zirconia that associate by relatively weakintermolecular forces that cause the silica nanoparticles and zirconiato clump together, even when dispersed in the polymerizable component ofthe present disclosure. The silica nanoparticles and zirconia (the“primary particles” that form the silica-zirconia nanoclusters) can havea mean diameter of 1 nanometer (nm) to 200 nm, where the resultingsilica-zirconia nanoclusters can have a longest dimension in themicrometer range (e.g., 10 micrometers) from the association or“nanocluster” of the silica nanoparticles and zirconia. The primaryparticles forming the silica-zirconia nanoclusters (e.g., the silicananoparticles and zirconia) can be grouped together in an amorphouscluster formation. The cluster formation of the silica nanoparticles andzirconia, however, is not limited to such an amorphous clusterformation.

Silica-zirconia nanoclusters may be prepared by mixing a nanosilica soltogether with a preformed nanozirconia particulate sol or a zirconiumsalt (e.g., an acetate or nitrate salt) solution. When a nanozirconiasol is used it is typically composed of crystalline zirconiananoparticles. The nanosilica sol typically comprises silica particleshaving a mean diameter from 1 to 200 nm, more typically 10 nm to 100 nm,even more typically from 15 nm to 60 nm, most typically from 15 nm to 35nm, with a mean particle diameter of about 20 nm being particularlywell-suited for fabrication of the silica-zirconia nanoclusters.

The zirconia sol typically comprises zirconia particles that are smallenough to not scatter the majority of visible light, but are largeenough to refract shorter wavelength blue light to give the opalescenteffect. A zirconia sol having a mean particle size from about 3 nm toabout 30 nm is suitable for forming the silica-zirconia nanoclusters.Typically, the zirconia particles in the sol have a mean particlediameter from 5 nm to 15 nm, more typically from 6 nm to 12 nm, and mosttypically from 7 nm to 10 nm. When mixed together under acidicconditions where the sol mixture is stable, such as at a pH of below 2,the preformed zirconia nanoparticles form a structure with the silicananoparticles on gelling and drying that gives the desired opalescencecharacter while maintaining a high level of optical translucency of thefinal composite material.

NALCO 1042 silica sol (Ecolab, Inc., St. Paul, Minn.), NALCO 1034A, orother commercially available colloidal silica sols may be used. If abase-stabilized sol is used, typically it will first be subjected to ionexchange in order to remove sodium, for example, with an AMBERLITEIR-120 ion exchange resin, or pH adjusted with nitric acid. It isusually desirable to pH adjust the silica to below 1.2, typically about0.8 to about 1.0, and then add the zirconia to it slowly, to preventlocalized gelation and agglomeration. The pH of the resultant mixture istypically about 1.1 to about 1.2. Suitable colloidal silica sols areavailable from a variety of vendors, including Nalco (Ecolab), H. C.Stark, Nissan Chemical (Snowtex), Nyacol, and Ludox (DuPont). Theselected sol should have silica particles that are discrete and of theappropriate size specified herein. The silica sol may be treated toprovide a highly acidic silica sol (e.g., nitrate stabilized) that canbe mixed with the zirconia sol without gelation.

The zirconia sol may be obtained using a process described, for example,in U.S. Pat. No. 6,376,590 (Kolb, et al.), or U.S. Pat. No. 7,429,422(Davidson et al.) the disclosures of which are incorporated by referenceherein. As used herein, the term “zirconia” refers to variousstoichiometries for zirconium oxides, most typically ZrO₂, and may alsobe known as zirconium oxide or zirconium dioxide. The zirconia maycontain up to 30 weight percent of other chemical moieties such as, forexample, Y₂O₃ and organic material.

The silica-zirconia nanoclusters can be prepared by mixing together thenanosilica sol with the nanozirconia sol, and heating the mixture to atleast 450° C. Typically, the mixture is heated for 4 to 24 hours at atemperature between about 400 to about 1000° C., more typically fromabout 450 to about 950° C., to remove water, organic materials, andother volatile components, as well as to potentially weakly aggregatethe particles (not required). Alternatively, or in addition, the solmixture may undergo a different processing step to remove water andvolatiles. The resulting material may be milled or ground and classifiedto remove large aggregates. The silica-zirconia nanoclusters may then besurface treated with, for example, a silane prior to mixing with apolymerizable component.

The composite material of the present disclosure can also include,optionally, one or more of filler particles in addition to the ceramicfibers. Such filler particles may be selected from one or more of a widevariety of materials suitable for incorporation in composite materialsused for dental applications, such as filler particles currently used indental restorative compositions, and the like. The choice of the fillerparticle can affect properties of the composite material such as itsappearance, radiopacity and physical and mechanical properties.Appearance is affected in part by adjustment of the amounts and relativerefractive indices of the ingredients of the composite, thereby allowingalteration of the translucence, opacity or pearlescence of thecomposite. In this way, the appearance of the composite material can, ifdesired, be made to closely approximate the appearance of naturaldentition.

Filler particles may be selected from one or more of material suitablefor incorporation in compositions used for medical applications, such asfiller particles currently used in dental restorative compositions andthe like. The maximum particle size (the largest dimension of aparticle, generally, the diameter) of the filler particles is typicallyless than 20 micrometers, more typically less than 10 micrometers, andmost typically less than 5 micrometers. The number average particle sizediameter of the filler particles is typically no greater than 100 nm,and more typically no greater than 75 nm. The filler particles can havea unimodal or polymodal (e.g., bimodal) particle size distribution. Thefiller particles can be an inorganic material. It can also be acrosslinked organic material that is insoluble in the polymerizablecomponent, and is optionally filled with inorganic filler. The fillerparticle should in any event be suitable for use in the mouth. Thefiller particle can be radiopaque, radiolucent or non-radiopaque. Thefiller particle typically is substantially insoluble in water. Thefiller particle may have a variety of shapes, including but not limitedto equiaxed, spherical, polyhedral, oblong, lenticular, toroidal orwhisker.

Examples of suitable filler particles are naturally-occurring orsynthetic materials such as quartz, nitrides (e.g., silicon nitride);glasses containing, for example Ce, Sb, Sn, Sr, Ba, An, and Al;colloidal silica; feldspar; borosilicate glass; kaolin; talc; titania;and zinc glass; low Mohs hardness fillers such as those described inU.S. Pat. No. 4,695,251; and submicrometer silica particles (e.g.,pyrogenic silicas such as the “Aerosil” Series “OX 50”, “130”, “150” and“200” silicas sold by Degussa Akron, Ohio and “Cab-O-Sil M5” silica soldby Cabot Corp. Tuscola, Ill.) and non-vitreous microparticles of thetype described in U.S. Pat. No. 4,503,169. Silane-treatedzirconia-silica (Zr—Si) filler particles are especially useful incertain embodiments.

Metallic filler particles may also be incorporated, such as metal fillerparticles made from a pure metal such as those of Groups 4, 5, 6, 7, 8,11, or 12, aluminum, indium, and thallium of Group 13, and tin and leadof Group 14, or alloys thereof, where the elements from the recitedGroups are found in the 8 Jan. 2016 version of the IUPAC Periodic Table.Conventional dental amalgam alloy powders, typically mixtures of silver,tin, copper, and zinc, may also optionally be incorporated. The metallicfiller particles preferably have a number average particle size diameterof about 1 micrometer to about 100 micrometers, more preferably 1micrometer to about 50 micrometers. Mixtures of these filler particlesare also contemplated, as well as combination filler particles made fromorganic and inorganic materials.

Preferably, the composite material can include, when present, up to 12wt. % of nanoparticles as the filler particles based on the total weightof the composite material. For example, the composite material caninclude 2 to 12 wt. % of nanoparticles as the filler particles based onthe total weight of the composite material. As defined herein, thenanoparticles are discrete non-fumed metal oxide nanoparticles. Asdiscussed herein, for a given combination of components that forms thecomposite material the wt. % of each of the components adds to 100 wt. %(wt. % based on the total weight of the composite material). Examples ofdiscrete non-fumed metal oxide nanoparticles include discrete non-fumedheavy metal oxide nanoparticles. In addition, the discrete non-fumedmetal oxide nanoparticles can include both discrete non-fumed heavymetal oxide nanoparticles and discrete non-fumed non-heavy metal oxidenanoparticles. Examples of discrete non-fumed non-heavy metal oxidenanoparicles include nanosilica, while examples of discrete non-fumedheavy metal oxide nanoparticles include zirconia, yttria and lanthanaparticles. Discrete non-fumed heavy metal oxide nanoparticles may beprepared from heavy metal oxide sols as described according to U.S. Pat.No. 6,736,590 (Kolb et al.) or U.S. Pat. No. 7,429,422 (Davidson etal.). Discrete non-fumed non-heavy metal oxides may be purchased ascolloidal silica. The discrete non-fumed nanoparticles of silica may beprepared from dispersions, sols, or solutions of at least one precursor.Processes of this nature are described, for example, in U.S. Pat. No.4,503,169 (Randklev) and GB Patent No. 2291053 B. The discrete non-fumedmetal oxide nanoparticles may also be surface treated with, for example,a silane prior to mixing with a polymerizable component.

The discrete non-fumed metal oxide nanoparticles are typically finelydivided with a unimodal or polymodal (e.g., bimodal) particle sizedistribution. The maximum particle size (the largest dimension of aparticle, generally, the diameter) of the discrete non-fumed metal oxidenanoparticles is typically 5 nm to 200 nm, more typically 5 nm to 100nm, and most typically 5 nm to 80 nm.

Other suitable filler particles are disclosed in U.S. Pat. No. 6,387,981(Zhang et al.); U.S. Pat. No. 6,572,693 (Wu et al.); U.S. Pat. No.6,730,156 (Windisch); and U.S. Pat. No. 6,899,948 (Zhang); U.S. Pat. No.7,022,173 (Cummings et al); U.S. Pat. No. 6,306,926 (Bretscher et al);U.S. Pat. No. 7,030,049 (Rusin et al); U.S. Pat. No. 7,160,528 (Rusin);U.S. Pat. No. 7,393,882 (Wu et al); U.S. Pat. No. 6,730,156 (Windisch etal); U.S. Pat. No. 6,387,981 (Zhang et al); U.S. Pat. No. 7,090,722(Budd et al); U.S. Pat. No. 7,156,911 (Kangas et al); U.S. Pat. No.7,361,216 (Kolb et al); as well as in International Publication No. WO03/063804 (Wu et al.), incorporated herein by reference. Fillerparticles described in these references include nanosized silicaparticles, nanosized metal oxide particles, and combinations thereof.Nanofillers are also described in U.S. Pat. No. 7,085,063 (Kangas etal.); U.S. Pat. No. 7,090,721 (Craig et al.) and U.S. Pat. No. 7,649,029(Kolb et al.); and U.S. Patent Publication Nos. 2010/0089286 (Craig etal); US 2011/0196062 (Craig et al), all incorporated herein byreference. As discussed herein, the surface of the filler particles may,optionally, be treated with a surface treatment, as discussed herein, inorder to enhance the bond between the filler and the polymerizablecomponent. In addition, the ceramic fibers and filler particles, whenfiller particles are present, may be modified with more than one (e.g.,two or more) of the surface treatments discussed herein (e.g., couplingagents and/or surface treatments). For example, the same surfacetreatments may be used for each of the ceramic fibers, while differentsurface treatments may be used for the filler particles, when present.Different surface treatments may also be used for two or more groups ofthe ceramic fibers and filler particles, when present in the compositematerial. For example, the ceramic fibers to be used in the compositematerial can include a first group of the ceramic fibers that have asurface treatment that is compositionally different than a second groupof the ceramic fibers used in the composite material.

As discussed herein, to achieve good aesthetics in a composite material,the optical properties of the components of the composite need to behighly matched. Examples of such optical properties for the componentsinclude not only the shade and the color of the components, but also howwell the refractive index of the fillers (e.g., the ceramic fibers)match the refractive index of the hardened polymerizable component.Matching the refractive index of the components helps to minimize thescattering of light as it passes through the material, thereby helpingto provide a more translucent material. So, for example, the ceramicfibers of the present disclosure preferably have a refractive indexvalue within 0.1 or less of the refractive index of the hardenedpolymerizable component. More preferable is where the ceramic fibers ofthe present disclosure preferably have a refractive index value within0.05 or less of the refractive index of the hardened polymerizablecomponent. Most preferable is where the ceramic fibers of the presentdisclosure preferably have a refractive index value within 0.005 or lessof the refractive index of the hardened polymerizable component.

Examples of refractive index values for the ceramic fibers includeceramic fibers have a refractive index value of 1.40 to 1.65.Preferably, the refractive index value of the ceramic fibers is 1.50 to1.58. Most preferably, the refractive index value of the ceramic fibersis 1.52 to 1.56. A preferred method for adjusting the refractive indexof the ceramic fibers is by altering the ratio of oxide of silicon toceramic metal oxide. The ceramic fibers refractive index can beapproximately predicted by interpolation based on a comparison of therelative volume percent of silica to ceramic metal oxide in the startingmixtures. When additional filler(s) are used with the ceramic fiberstheir refractive index values can also be matched within the rangesprovided herein.

The composite material of the present disclosure can be prepared bycombining all the various components using conventional mixingtechniques. The resulting composite material may optionally containadditional fillers (in addition to the ceramic fibers and nanoclusters),solvents, water, and/or other additives as described herein. Typically,photopolymerizable composite materials of the disclosure are prepared byadmixing, under “safe light” conditions, the components of the compositematerial. Suitable inert solvents may be employed if desired whenaffecting this mixture. A solvent may be used which does not reactappreciably with the components of the composite material.

Examples of suitable solvents include alcohols (e.g., propanol,ethanol), ketones (e.g., acetone, methyl ethyl ketone), esters (e.g.,ethyl acetate), other nonaqueous solvents (e.g., dimethylformamide,dimethylacetamide, dimethylsulfoxide, 1-methyl-2-pyrrolidinone)), ormixtures thereof. If desired, the composite material of the disclosuremay contain additives such as indicators, dyes (includingphotobleachable dyes), pigments, inhibitors, accelerators, viscositymodifiers, wetting agents, antioxidants, tartaric acid, chelatingagents, buffering agents, stabilizers, diluents, and other similaringredients that will be apparent to those skilled in the art.Surfactants, for example, nonionic surfactants, cationic surfactants,anionic surfactants, and combinations thereof, may optionally be used inthe compositions. Useful surfactants include non-polymerizable andpolymerizable surfactants.

Additionally, medicaments or other therapeutic substances can beoptionally added to the composite material. Examples include, but arenot limited to, fluoride sources, whitening agents, anticaries agents(e.g., xylitol), remineralizing agents (e.g., calcium phosphatecompounds and other calcium sources and phosphate sources), enzymes,breath fresheners, anesthetics, clotting agents, acid neutralizers,chemotherapeutic agents, immune response modifiers, thixotropes,polyols, anti-inflammatory agents, antimicrobial agents, antifungalagents, agents for treating xerostomia, desensitizers, and the like, ofthe type often used in dental restorative materials. Combination of anyof the above additives may also be employed. The selection and amount ofany one such additive can be selected by one of skill in the art toaccomplish the desired result without undue experimentation.

The amounts and types of each ingredient in the composite material canbe adjusted to provide the desired physical and handling propertiesbefore and after polymerization. For example, the polymerization rate,polymerization stability, fluidity, compressive strength, tensilestrength and durability of the dental restorative material typically maybe adjusted, in part, by altering the types and amounts ofpolymerization initiator(s) and the loading and particle sizedistribution of filler(s). Such adjustments typically are carried outempirically based on previous experience with composite materials. Whenthe composite material is used in a dental application, any toothsurface receiving the composite material can optionally be pre-treatedwith a primer and/or an adhesive by methods known to those skilled inthe art.

The composite material can be supplied in a variety of forms includingone-part systems and multi-part systems, e.g., two-part paste/pastesystems. Other forms employing multi-part combinations (i.e.,combinations of two or more parts), each of which is in the form of apowder, liquid, gel, or paste are also possible. The various componentsof the composite material may be divided up into separate parts inwhatever manner is desired; however, in a redox multi-part system, onepart typically contains the oxidizing agent and another part typicallycontains the reducing agent, though it is possible to combine thereducing agent and oxidizing agent in the same part of the system if thecomponents are kept separated, for example, through use ofmicroencapsulation.

The components of the composite material can be included in a kit, wherethe contents of the composite material are packaged in at least onecontainer to hold the composite material and allow for storage of thecomponents until they are needed. More than one of the compositematerials discussed herein can be included in the kit. In addition tothe composite material(s) of the present disclosure, the kit can alsoinclude at least one dental component selected from the group of acement, an adhesive, an abrasive, a polishing paste, an instrument,software, a mill, a CAD/CAM system, a composite, a porcelain, a stain, abur, an impression material, a dental mill blank or a combinationthereof.

The components of the composite material can be mixed and clinicallyapplied using conventional techniques. A curing light is generallyrequired for the initiation of photopolymerizable composite materials.The composite material may be in the form of composites or restorativesthat adhere very well to dentin and/or enamel. Optionally, a primerlayer can be used on the tooth tissue on which the composite material isused.

The composite material of the present disclosure can be hardended tomake a dental product. Hardening the composite material can beaccomplished based on the type of dental product being produced. Forexample, the composite material can be hardened, when appropriate, usingheat, light, microwave, e-beam, fusing or chemical cure. Once hardened,the dental product and/or dental mill blank of the present disclosurecan be trimmed if necessary; and optionally, mounted on a holder stub orpost if necessary. The dental product can be selected from the groupconsisting of a dental restorative (e.g., a sealant, an inlay, an onlayor a bridge), a dental adhesive, a dental mill blank, a dental cement, adental prostheses, an orthodontic device, an orthodontic adhesive, adental casting material, artificial crowns, anterior fillings, posteriorfillings, and cavity liners or a dental coating.

The dental mill blank of the present disclosure is a block (threedimensional article) of material from which a dental article can bemachined. A dental mill blank may have a size suitable for the machiningof one or more dental articles. The dental mill blank of the presentdisclosure can also include a mounting post or frame to facilitateaffixation of the blank in a milling machine for milling a dentalrestorative. A mounting post or frame functions as handle by which ablank is held as it undergoes the milling process. An example of adevice for such milling processes can include a CAM machine controlledby data provided by a CAD system (e.g., a CNC machine) for the shape ofthe desired dental article. These machines produce dental prostheses bycutting, milling, and grinding the near-exact shape and morphology of arequired restorative with greater speed and lower labor requirementsthan conventional hand-made procedures. By using a CAD/CAM millingdevice, the prosthesis can be fabricated efficiently and with precision.Other machining process can include abrading, polishing, controlledvaporization, electronic discharge milling (EDM), cutting by water jetor laser or other method of cutting, removing, shaping or millingmaterial. After milling, some degree of finishing, polishing andadjustment may be necessary to obtain a custom fit into the mouth and/oraesthetic appearance.

The composite material of the present disclosure can also be used nearor on a tooth surface. For example, the composite material can be placednear or on a tooth surface, where the shape or topography of thecomposite material near or on the tooth surface can be changed prior tohardening the composite material. Changing the shape of the compositematerial near or on the tooth surface can include shaping the compositematerial into a dental product selected from the group consisting of adental prostheses, an orthodontic device, a dental crown, an anteriorfilling, a posterior filing or a cavity liner. These steps can befollowed sequentially or in a different order. For example, in apreferred embodiment where the dental restorative material is a dentalmill blank or a prosthesis, the hardening step is generally completedprior to changing the topography of the material. Changing thetopography of the material can be accomplished in various ways,including manual manipulation using hand held instruments, or by machineor computer aided apparatus, such as a CAD/CAM milling machine in thecase of prostheses and dental mill blanks. Optionally, a finishing stepcan be performed to polish, finish, or apply a coating on the dentalrestorative material.

The features and advantages of this disclosure are further illustratedby the following examples, which are in no way intended to be limitingthereof. The particular materials and amounts thereof recited in theseexamples, as well as other conditions and details, should not beconstrued to unduly limit this disclosure. Unless otherwise indicated,all parts and percentages are on a weight basis, all water is deionizedwater, and all molecular weights are weight average molecular weight.

EXAMPLES

Unless otherwise indicated, the methods discussed herein were performedat room temperature (23° C.) and at atmospheric pressure. All commercialmaterials were used as obtained from the vendor. Unless otherwisespecified, all materials are from Sigma-Aldrich Corp. (St. Louis, Mo.).

The testing methods use the following abbreviations: kg, kilogram; s,second(s); cm, centimeter; mm, millimeter; in., inch; min, minute(s);hr, hour; ° C., degree Celsius; %, percent; kN, kilonewton; MPa,megapascals; GPa, gigapascals; nm, nanometer; mW, milliwatt; rpm,rotations per minute; gf, gram-force; and RI, refractive index; psi,pounds per square inch gauge; ml, milliliter; g, grams; μm, micrometer;SEM, Scanning Electron Microscopy; LED, light emitting diode.

Testing Methods Sixty Degree Gloss

A sixty degree gloss was measured using a Novo-Curve (RhopointInstrument, St. Leonards-on-Sea, East Sussex, UK) per ASTM D2457.

Length Measurement—Optical Microscope

The length of the ceramic fiber was determined using an opticalmicroscope (Olympus MX61, Tokyo, Japan) fit with a CCD Camera (OlympusDP72, Tokyo, Japan) and analytic software (Olympus Stream Essentials,Tokyo, Japan). Samples were prepared by spreading representativesamplings of the ceramic fiber on a glass slide and measuring thelengths of at least 200 ceramic fibers at 10× magnification.

Average Surface Area—BET Gas Adsorption

Average surface area was measured using Brunauer-Emmitt-Teller (BET) gasadsorption. Use a Gemini V 2380 (Micromeritics, Norcross, Ga., USA) BETgas adsorption unit, which tests BET surface area using the staticvolumetric principle. The data was analyzed using Gemini V 2380 V1.00software, which determines surface area using various thermodynamicmodels and using a molecular statistics model based on non-localizedDensity Function Theory. Samples were prepared by soaking for 2 hours at350° C. under a dry N₂ gas purge.

Contrast Ratio (CR) Test Method

Samples of uncured composite material were formed into 1 mm thick by 30mm diameter disks using a stainless steel mold. The formed samples werepressed flat in a Carver Press at 10,000 to 15,000 psi between sheets ofmylar film. The disks were cured by exposing the disks to illuminationfrom an LED array (455 nm wavelength, 850 mW/cm² intensity—Clear StoneTechnology, Hopkins, Minn. USA: Control Unit CF2000, LED arrayJL2-455F-90) for 20 s on one side of the disk. ASTM-D2805-95 (HidingPower of Paints by Reflectometry) was modified to measure a disk. Thetest method measures the CR or visual opacity of a material.Y-tristimulus values for the disks of cured composite material weremeasured on a Color i7 spectrophotometer (X-Rite, Grand Rapids, Mich.,USA) with a 25 mm aperture using separate white and black backgrounds.All measurements were made in reflection mode with a D65 Illuminant withno filters. A 10 degree angle of view was used. CR was calculated as theratio of the Y-tristimulus of a cured composite material on a blacksubstrate to the Y-tristimulus through an identical material on a whitesubstrate (CR=R_(B)/R_(W)×100) in reflectance. Lower CR values areindicative of more translucent materials.

Flexural Strength and Flexural Modulus Test Method

Test Specimen were prepared by extruding uncured composite material intoa 2 mm×2 mm×25 mm quartz glass mold to form a test bar. The test bar ofthe composite material was cured in the quartz glass mold using twoXL3000 dental cure lights (3M ESPE, St. Paul, Minn., USA). The exitwindow of one light was placed over the center of the test bar and curedfor 20 s, then using the 2 lights in tandem, the exit windows of thelights were placed over the uncured ends of the test bar andsimultaneously cured the bar for 20 s. The test bar was flipped and thecure protocol repeated. The cured test bar of the composite material waspushed out of the quartz glass mold. The cured test bars of thecomposite material were submerged for about 24 hr in 37° C. deionizedwater prior to testing.

Flexural Strength and Flexural Modulus of the cured test bars of thecomposite material were measured on an Instron tester (Instron 5944,Instron Corp., Canton, Mass., USA) according to ANSI/ADA (AmericanNational Standard/American Dental Association) specification No. 27(1993) at a crosshead speed of 0.75 mm/min and a span of 20 mm. Theresults were reported in MPa for Flexural Strength and GPa for FlexuralModulus.

Fracture Toughness Test Method

Test Specimen were prepared by extruding uncured composite material intoa 3 mm×5 mm×25 mm quartz glass mold to form a test bar. The test bar ofthe composite material was cured in the quartz glass mold using twoXL3000 dental cure lights (3M ESPE, St. Paul, Minn., USA). The exitwindow of one light was placed over the center of the test bar and curedfor 20 s, then using the 2 lights in tandem, the exit windows of thelights were placed over the uncured ends of the test bar andsimultaneously cured the bar for 20 s. The test bar was flipped and thecure protocol repeated. The test bar of the cured composite material waspushed out of the quartz glass mold. Next, a notch was cut in the centerof the test bar with a wafering blade with a kerf of 0.15 mm (Buehler,Lake Bluff, Ill., USA) using an ISOMET Low Speed Saw (Buehler, LakeBluff, Ill., USA). The notch was approximately 2 mm deep. The cured testbars of the composite material were submerged for about 24 hr in 37° C.deionized water prior to testing.

Fracture Toughness was measured on an Instron tester (Instron 5944,Instron Corp., Canton Mass., USA) with a crosshead speed of 0.75 mm/min.The toughness was calculated per ASTM 399-05.

Gloss Retention After Toothbrush Abrasion Test Method

Samples of uncured composite were formed using a stainless steel moldinto 2 mm thick×21 mm long×10 mm wide tiles. The uncured composite waspressed flat between sheets of polyester film in a Carver Press (Wabash,Ind., USA) at 6000 to 10,000 psi and cured for 20 s in LED array with455 nm wavelength, 850 mW/cm² intensity (Clear Stone Technology,Hopkins, Minn., USA: Control Unit CF2000, LED array JL2-455F-90). Thesample was removed from mold and polish to high gloss using an Ecomet 4Variable Speed Grinder—Polisher fit with an Automet 2 Power Head(Buehler, Lake Bluff, Ill., USA). High gloss was achieved through theuse of consecutively finer grinding and polishing media. First, 320 gritsilicon carbide sandpaper was used followed by 600 grit silicon carbidesandpaper (sandpaper from 3M, St. Paul, Minn., USA). Next, 9 micrometerdiamond paste was used followed by 3 micrometer paste, and finally 0.05micrometer polishing slurry was used (polishing paste and slurrypurchased from Buehler, Lake Bluff, Ill., USA). The tiles were storedfor about 24 hrs submerged in 37° C. water.

The polish retention of the tiles was measured by challenging thepolished surface by toothbrush abrasion. The tile was affixed in a jig,gloss side up. The initial gloss was measured (see “Sixty DegreeGloss”). The jig was placed in a well in an automated brushing machinewhere 5 ml of abrasive slurry consisting of 1 to 1 Crest RegularToothpaste (P&G, Cincinnati, Ohio, USA) and water was placed over thetile. The tile was then brushed under a load of 450 gf with a 47 tuftAcclean toothbrush (Henry Schein, Melville, N.Y., USA). The tiles weresubjected to 6000 total brush cycles, with the gloss measured every 1500cycles. Five ml of fresh slurry were added after every glossmeasurement.

Polishability Test Method

Tiles of the cured composite material were formed as discussed above forthe Gloss Retention after Toothbrush Abrasion Test Method. The surfaceof the tile was uniformly roughened with 320 grit silicon carbide sandpaper. The roughened surface was polished using a Sof-Lex™ SpiralFinishing Wheel and a Sof-Lex™ Spiral Polishing Wheel (3M ESPE St. Paul,Minn., USA). A mechanical arm was fit with a dental hand piece toprovide constant motion and force (60 gf) for the Sof-Lex™ SpiralFinishing Wheel or the Sof-Lex™ Spiral Polishing Wheel. The roughenedtiles were finished and polished for 1 min at 1500 rpm with each wheel.Sixty degree gloss of the surface of the cured composite was measured(see Sixty Degree Gloss) after the polishing step.

Materials

“BisEMA-6” refers to ethoxylated (6 mole ethylene oxide) bisphenol Adimethacrylate as further described in U.S. Pat. No. 6,030,606,available from Sartomer Co., Inc. (Exton, Pa.) as “CD541”;

“BisGMA” refers to2,2-bis[4-(2-hydroxy-3-methacryloyloxypropoxy)phenyl]propane (alsoreferred to as bisphenol A diglycidyl ether methacrylate), CAS Reg. No.1565-94-2.

“BHT” refers to butylated hydroxytoluene(2,6-di-tert-butyl-4-methylphenol), CAS Reg. No. 128-37-0;

“BZT” refers to2-(2′-hydroxy-5′-methacryloxyethylphenyl)-2H-benzotriazole, CAS Reg. No.96478-09-0, available from Ciba, Inc. (Tarrytown, N.Y.) as “TINUVIN®796”, also available from Sigma-Aldrich Corp. (St. Louis, Mo.);

“CPQ” refers to camphorquinone, CAS Reg. No. 10373-78-1;

“DPIHFP” or “DPIPF6” refers to diphenyliodonium hexafluorophosphate, CASReg. No. 58109-40-3, available from Johnson Matthey, Alfa Aesar Division(Ward Hill, Mass.);

“EDMAB” refers to ethyl 4-dimethylaminobenzoate, CAS Reg. No.10287-53-3;

“ENMAP” refers to ethyl N-methyl-N-phenyl-3-aminopropionate (alsoreferred to as N-methyl-N-phenyl-beta-alanine ethyl ester), CAS Reg. No.2003-76-1, which can be prepared by known methods, such as thosedescribed by Adamson, et al.; JCSOA9; J. Chem. Soc.; 1949; spl. 144-152,which is incorporated herein by reference; also available from JohnsonMatthey, Alfa Aesar Division (Ward Hill, Mass.);

“GENIOSIL GF-31” or “GF-31” refers to3-methacryloxypropyltrimethoxysilane, available from Wacker Chemie AG(Munich, Germany);

“IRGACURE 819” refers to a bis(2,4,6-trimethylbenzoyl)phenylphosphineoxide photoinitiator, CAS Reg. No. 162881-26-7, available from CibaSpecialty Chemicals Corp. (Tarrytown, N.Y.), also available fromSigma-Aldrich Corp. (St. Louis, Mo.);

“PEG600 DM” refers to poly(ethylene glycol) dimethacrylate, average MW˜600, obtained from Sartomer Co., Inc. (Exton, Pa.);

“PROCRYLAT” refers to 2,2-bis-4-(3-methacryloxypropoxy)phenyl)propanedimethacrylate, CAS Reg. No. 27689-12-9, as further described inWO2006/020760;

“TEGDMA” refers to triethyleneglycol dimethacrylate, CAS Reg. No.109-16-0, available from Sartomer Co., Inc. (Exton, Pa.);

“UDMA” refers to diurethane dimethacrylate, CAS Reg. No. 72869-86-4,obtained under the trade designation “ROHAMERE 6661-0” from Rohm AmericaLLC (Piscataway, N.J.); also available from Dajac Laboratories (Trevose,Pa.);

Fillers

“S/T Silica/Zirconia Nanoclusters” refers to silane-treatedsilica-zirconia nanocluster filler, prepared essentially as described inU.S. Pat. No. 6,730,156 at column 25, lines 50-63 (Preparatory ExampleA) and at column 25, line 64 through column 26, line 40 (PreparatoryExample B) with minor modifications, including performing thesilanization in 1-methoxy-2-propanol (rather than water) adjusted to apH of about 8.8 with NH₄OH (rather than to a pH of 3-3.3 withtrifluoroacetic acid), and obtaining the S/T Silica/Zirconia Clusters bygap drying (rather than spray drying).

“S/T Zirconia/Silica Filler” refers to zirconia-silica filler (which canbe prepared as described in U.S. Pat. No. 6,624,211 at column 15, line60 through column 16, line 28) silane-treated in the following manner.Mix one hundred parts of the filler with deionized water at a solutiontemperature of between 20-30° C. Adjust the pH of the resulting slurryto 3-3.3 with trifluoroacetic acid (0.278 parts). Add 7 parts (based onthe one hundred parts of the filler) of3-methacryloxypropyltrimethoxysilane (available from Wacker Chemie AG,Munich, Germany) to the slurry. Mix the slurry for 2 hrs. At the end of2 hrs, neutralize the pH of the slurry with calcium hydroxide. Recoverthe S/T Zirconia/Silica by drying, crushing and screening through a 74micrometer screen.

“S/T 20 nm Silica Nanoparticle” refers to silane-treated silicananoparticle filler having a nominal particle size of approximately 20nanometers, prepared essentially as described in U.S. Pat. No. 6,572,693at column 21, lines 63-67 (Nano-sized particle filler, Type #2); “S/TNanozirconia Nanoparticle” refers to silane-treated zirconiananoparticle filler, which can be prepared from the zirconia sol asgenerally described in U.S. Pat. No. 8,647,510 at column36 line 61 tocolumn 37 line 16 (Example 11A-IER). The zirconia sol is added to anequivalent weight of 1-methoxy-2-propanol containing3-methacryloxypropyltrimethoxysilane (1.1 mmol of3-methacryloxypropyltrimethoxysilane per gram of nanozirconia to besurface treated). The mixture is heated to about 85° C. for 3 hours withstirring. The mixture is cooled to 35° C., adjusted to a pH of about 9.5with NH₄OH, and the mixture reheated to about 85° C. for 4 hours withstirring. The resultant S/T Nanozirconia is isolated by removingsolvents via gap drying. S/T Nanozirconia may also be prepared asdescribed in U.S. Pat. No. 7,649,029 beginning at column 19, line 39through column 20, line 41 (Filler I), except for the substitution of3-methacryloxypropyltrimethoxysilane for the blend of Silquest A-174 andA-1230, and further removing the solvents via gap drying.

Ceramic Fiber

Ceramic Fiber 0

Amorphous aluminoborosilicate ceramic fibers with diameters of 10-12 μm(available from 3M Company as NEXTEL™ 312, approximate composite of62.5% Al₂O₃, 24.5% SiO₂, 13% B₂O₃, Denier of 3,600 g/9,000 m, RI of1.568) were chopped to a relatively narrow length distribution. Thechopped ceramic fibers were heat treated at 700° C. in air for 1 to 4hours to remove organic coatings to provide Ceramic Fiber 0.

Ceramic Fiber 0 had an average surface area of <0.5 m²/g as measured byBET gas adsorption. The ceramic fiber length, as discussed above in thedetailed description, is giving by the fraction of the chopped ceramicfibers that are either less than or equal to than a given “L” ceramicfiber length value. As discussed herein, these values are denoted by “L”values (e.g., L10, L25, L50, L75, L90 and L99) where the numberfollowing the “L” indicates the percentage (based on a total number ofthe ceramic fibers) of the ceramic fibers (for a given number of ceramicfibers) that have a length that is either less than or equal to a given“L” length value.

For Ceramic Fiber 0, the L50 (median) length value was 147 μm, the L10length value was 106 μm, the L25 length value was 131 μm, the L75 lengthvalue was 157 μm and the L90 length value was 168 μm.

Ceramic Fiber 1

Ceramic Fiber 0 (20.0017 g) was dispersed in a mixture of ethyl acetate(23.1 g), GF-31 (0.0213 g), and 30% aqueous ammonium hydroxide solution(0.54 g). The dispersion was stirred overnight at room temperature (23°C.). The ceramic fibers were then flash dried in a fume hood and heatedto 80° C. for 30 minutes to provide Ceramic Fiber 1 (surface modified).The L10, L25, L50, L75, and L90 length values for Ceramic Fiber 1 weresubstantially the same as those listed for Ceramic Fiber 0.

Ceramic Fiber 2

Ceramic Fiber 2 were prepared in a fashion similar to Ceramic Fiber 1,except that prior to surface modification with GF-31, the ceramic fiberswere subjected to a boiling water treatment as follows. The ceramicfibers (508 g) were dispersed in deionized water and boiled for 120 min.The boiled ceramic fibers were recovered by filtration and then dried.Analysis of the boiled ceramic fibers by BET gas adsorption indicated asurface area of about 23 m²/g.

The boiled ceramic fibers (302.1 g) were dispersed in a mixture of ethylacetate (399.2 g), GF-31 (6.8 g), and 30% aqueous ammonium hydroxidesolution (6.0 g). The dispersion was stirred overnight at roomtemperature (23° C.). The ceramic fibers were flash dried in a fume hoodand then heated to 80° C. for 30 minutes to provide Ceramic Fiber 2. TheL10, L25, L50, L75, and L90 length values for Ceramic Fiber 2 weresubstantially the same as those listed for Ceramic Fiber 0.

Ceramic Fiber 3

Alumina ceramic fibers with diameters of 10-12 μm (available from 3MCompany as NEXTEL™ 610, >99% α-Al₂O₃, Denier of 10,000 g/9,000 m, RI of1.74) were chopped to a relatively narrow length distribution. Thechopped ceramic fibers were heat cleaned at 700° C. in air for 1-4 hoursto remove organic coatings to provide base ceramic fibers. The ceramicfibers had an average surface area of <0.2 m²/g taken from materialsproperty sheet and an arithmetic mean length of 190 μm with a standarddeviation of 30 μm according to SEM measurements provided by the ceramicfiber processor. The base ceramic fibers were silane treated asdescribed for Ceramic Fiber 1 to provide Ceramic Fiber 3. For CeramicFiber 3, the L50 (median) length value was 130 μm, the L10 length valuewas 51 μm, the L25 length value was 79 μm, the L75 length value was 173μm and the L90 length value was 220 μm.

Ceramic Fiber 4

Alumina-silica ceramic fibers with diameters of 10-12 μm (available from3M Company as NEXTEL™ 720, approximately 85% Al₂O₃ and 15% SiO₂, Denierof 10,000 g/9,000 m) were chopped to a relatively narrow lengthdistribution. The chopped ceramic fibers were heat cleaned at 700° C. inair for 1-4 hours to remove organic coatings to provide the base ceramicfibers. The base ceramic fibers had an average surface area of <0.2 m²/gtaken from materials property sheet and an arithmetic mean length of 180μm with a standard deviation of 40 μm according to SEM measurementsprovided by the ceramic fiber processor. The base ceramic fibers weresilane treated as described for Ceramic Fiber 1 to provide Ceramic Fiber4. For Ceramic Fiber 4, the L50 (median) length value was 163 μm, theL10 length value was 55 μm, the L25 length value was 132 μm, the L75length value was 188 μm and the L90 length value was 207 μm.

Ceramic Fiber 5

Amorphous aluminoborosilicate ceramic fibers with diameters of 10-12 μm(available from 3M Company as NEXTEL™ 312, approximate composite of62.5% Al₂O₃, 24.5% SiO₂, 13% B₂O₃, Denier of 3,600 g/9,000 m, RI of1.568) were chopped to a relatively narrow length distribution. Thechopped ceramic fibers were heat cleaned at 700° C. in air for 1-4 hoursto remove organic coatings to provide Ceramic Fiber 5. Ceramic Fiber 5had an average surface area of <0.2 m²/g taken from materials propertysheet and an arithmetic mean length of 2950 μm with a standard deviationof 120 μm according to SEM measurements taken from Ceramic Fiber 5. Dueto the large lengths for Ceramic Fiber 5, the L90 length value wasassumed to be greater than 500 μm.

Ceramic Fiber 6

Ceramic Fiber 6 was formed by milling Ceramic Fiber 0 as follows. Asmall scale jar mill (Roalox Model 774, size 000, Gardco, a Paul NGardner Company, Pompano Beach, Fla., USA) was filled with 400 g of ⅜″yttria stabilized zirconia rod milling media and 50.41 g of CeramicFiber 0, and the ceramic fibers milled for 2 hours at 250 rpm. Themedian ceramic fiber length of Ceramic Fiber 6 was 45 μm when measuredwith an optical microscope, the L10 value was 27 μm, the L25 value was34 μm, the L75 value was 59 μm and the L90 value was 77 μm.

As more fully detailed below, the composite materials of the presentdisclosure include ceramic fibers as a filler material. The compositematerials of the present disclosure display excellent handlingcharacteristics. The cured composite materials of the present disclosurealso display significant increases in mechanical performance (e.g.,fracture toughness and flexural modulus among others) in comparison tocured composite materials that lack ceramic fiber filler altogether, orlacked a ceramic fiber filler with an appropriate length and/or lengthdistribution. The increase in mechanical performance of the compositematerials of the present disclosure may be particularly useful in dentalapplications, such as in the posterior regions of the mouth where thereis a need for highly durable restorations. Additionally, the ceramicfibers of the composite materials of the present disclosure haverefractive indices which can match the hardened polymerizable componentof the composite system, thereby providing a composite material fromwhich highly aesthetic restorations may be prepared. Finally, curedcomposite materials of the present disclosure provided excellentpolishability and polish retention characteristics.

Composite Material

A first polymerizable component, Resin 1, was prepared by mixing thecomponents shown in Table 1 at 45° C. until all of the components areuniformly mixed. Resin 1 was used to prepare composite materials withrheological properties similar to typical universal (sculptable) dentalcomposites.

TABLE 1 Polymerizable Component - Resin 1 Component wt. % BisGMA 24.575%TEGDMA 1.182% UDMA 34.401% BisEMA-6 34.401% PEG600 DM 3.736% CPQ 0.220%DPIHFP 0.350% IRGACURE 819 0.050% ENMAP 0.810% BHT 0.150% BZT 0.125%

A second polymerizable component, Resin 2, was prepared by mixing thecomponents shown in Table 2 until all of the components are uniformlymixed. Resin 2 was used to prepare composite materials with rheologicalproperties similar to typical flowable dental composites.

TABLE 2 Polymerizable Component - Resin 2 Component wt. % BisGMA 26.27%TEGDMA 15.76% PROCRYLAT 56.22% CPQ 0.16% DPIHFP 0.30% EDMAB 0.60% BHT0.09% BZT 0.60%

Examples of the composite materials were prepared by mixing thecomponents shown in Table 3 until uniform. In all cases, the compositematerials displayed acceptable handling characteristics.

TABLE 3 Composite Material Formulations for Universal (Sculptable) andFlowable Dental Composites Containing Varying Levels of Ceramic Fiber 0and Nanoclusters Composite Material S/T 20 S/T nm S/T S/T NanozirconiaSilica Silica/Zirconia Zirconia/Silica Ceramic Example (Ex)/Compar-Resin 1 Resin 2

Nanoclusters Filler Fiber 0 ative Example (CE) (wt. %) (wt. %) (wt. %)(wt. %) (wt. %) (wt. %) (wt. %) CE A* (Paste 1) 21.0 0.0 4.1 7.7 67.20.0 0.0 EX 1* (Paste 2) 21.0 0.0 3.9 7.4 63.7 0.0 4.0 EX 2* (Paste 3)21.0 0.0 3.7 6.9 60.5 0.0 7.9 EX 3* (Paste 4) 21.0 0.0 3.3 6.2 53.7 0.015.8 CE B* (Paste 5) 21.0 0.0 0.0 0.0 0.0 79.0 0.0 CE C* (Paste 6) 21.00.0 0.0 0.0 0.0 71.1 7.9 CE D^(§) (Paste 7) 0.0 35.0 0.0 7.2 57.8 0.00.0 EX 4^(§) (Paste 8) 0.0 35.0 0.0 5.0 40.0 0.0 20.0 EX 5^(§) (Paste 9)0.0 35.0 0.0 2.8 22.2 0.0 40.0 CE E^(§) (Paste 10) 0.0 35.0 0.0 0.0 0.065.0 0.0 CE F^(§) (Paste 11) 0.0 35.0 0.0 0.0 0.0 45.0 20.0 CE G^(§)(Paste 12) 0.0 35.0 0.0 0.0 0.0 25.0 40.0 *Universal (sculptable)formulations ^(§)Flowable formulations

 —Nanoparticle

The above identified composite materials (Table 3) were cured accordingto the methods described above and subjected to mechanical testing toevaluate the properties of the materials made with varying levels ofCeramic Fiber 0 and nanoclusters. Mechanical testing data is summarizedin Table 4, below.

TABLE 4 Fracture Toughness, Flexural Strength, Flexural Modulus, andPolish Retention Data for Selected Cured Composite Materials FractureFlexural Flexural Polish Ceramic Toughness, Strength Modulus, RetentionExample (EX) and Compar- Nanocluster Fiber 0 MPa · m^(0.5) MPa GPa 60°gloss unit ative Example (CE) filler? (wt. %) (Std. Dev.) (Std. Dev.)(Std. Dev.) (Std. Dev.) CE A* Yes 0 2.09 152.8 12.2 76.1 (0.11) (7.4)(0.3) (1.5) EX 1* Yes 4.0 2.29 149.7 13.7 Not (0.14) (10.9) (0.3) testedEX 2* Yes 7.9 2.41 159.3 14.9 63.7 (0.11) (6.2) (0.4) (2.1) EX 3* Yes15.8 2.66 172.2 17.2 59.2 (0.11) (10.3) (0.2) (2.3) CE B* No 0 2.32161.2 11.5 8.2 (0.22) (5.0) (0.4) (0.3) CE C* No 7.9 2.70 164.0 13.910.3 (0.17) (11.0) (0.3) (0.4) CE D^(§) Yes 0 Not 130.5 8.2 Not tested(7.9) (0.2) tested EX 4^(§) Yes 20 Not 139.3 13.0 Not tested (7.2) (0.4)tested EX 5^(§) Yes 40 Not 143.5 17.2 Not tested (5.4) (0.5) tested CEE^(§) No 0 Not 144.5 7.9 Not tested (10.7) (0.2) tested CE F^(§) No 20Not 130.3 12.9 Not tested (7.9) (0.2) tested CE G^(§) No 40 Not 120.716.9 Not tested (3.3) (0.6) tested *Univeral (sculptable) formulations^(§)Flowable formulations

As seen in Table 4, the addition of Ceramic Fiber 0 increases thefracture toughness and flexural modulus of the cured composite material(cf. CE A and EX 1), where the more Ceramic Fiber 0 that is added to thecomposition the larger the gain (cf. EX 1 and EX 3). While ceramicfibers such as Ceramic Fiber 0 provided cured composites with improvedmechanical properties, formulations which lacked nanocluster fillerprovided cured composites with poor polish retention properties (cf. EX2 and CE C). Table 4 also shows that incorporation of Ceramic Fiber 0into flowable composite formulations provides cured materials withimproved flexural modulus properties, nearing those of universal(sculptable) composites (cf. EX 5 and EX 3). This gives rise to thepotential for expanded indications of flowable composite materials.

Impact of Ceramic Fiber Treatments

TABLE 5 Composite Material Formulations for Universal (Sculptable) andFlowable Dental Composites Containing Varying Levels of Ceramic Fiber 0,Ceramic Fiber 1 (Surface Treated), or Ceramic Fiber 2 (Surface TreatedAfter Boiling) Composite Material S/T S/T S/T S/T 20 nm Silica/Zirconia/ Nanozirconia Silica Zirconia Silica Ceramic Ceramic CeramicExample (Ex)/Compar- Resin 1 Resin 2

Nanocluster Filler Fiber 0 Fiber 1 Fiber 2 ative Example (CE) (wt. %)(wt. %) (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) (wt. %) — CE A*(Paste 1) 21.0 0.0 4.1 7.7 67.2 0.0 0.0 0.0 0.0 EX 3* (Paste 4) 21.0 0.03.3 6.2 53.7 0.0 15.8 0.0 0.0 EX 6* (Paste 13) 22.0 0.0 4.1 7.6 50.7 0.00.0 15.6 0.0 EX 7* (Paste 14) 21.0 0.0 3.3 6.2 53.7 0.0 0.0 0.0 15.8 CED^(§) (Paste 7) 0.0 35.0 0.0 7.2 57.8 0.0 0.0 0.0 0.0 EX 5^(§) (Paste 9)0.0 35.0 0.0 2.8 22.2 0.0 40.0 0.0 0.0 EX 8^(§) (Paste 15) 0.0 35.0 0.02.8 22.2 0.0 0.0 0.0 40.0 CE E^(§) (Paste 10) 0.0 35.0 0.0 0.0 0.0 65.00.0 0.0 0.0 CE G^(§) (Paste 12) 0.0 35.0 0.0 0.0 0.0 25.0 40.0 0.0 0.0CE H^(§) (Paste 16) 0.0 35.0 0.0 0.0 0.0 25.0 0.0 0.0 40.0 *Univeral(sculptable) formulations ^(§)Flowable formulations

 —NanoparticleThe above identified composite materials (Table 5) were cured accordingto the methods described above and subjected to mechanical testing toevaluate the properties of the materials made with varying levels andtypes of chopped ceramic fibers. Mechanical testing data is summarizedin Table 6, below.

TABLE 6 Flexural Strength Data for Selected Cured Composite Materials -Impact of Surface Treatment of the Ceramic Fiber Example (EX) andCeramic Flexural Comparative Nanocluster fiber Strength MPa Example (CE)filler? (wt. %) (Std. Dev.) EX 1* Yes   15.8 171.9 (8.9) (Paste 2)(Ceramic Fiber 0) EX 7* Yes   15.8 181.9 (3.1) (Paste 14) Ceramic Fiber2) EX 6* Yes   15.6 183.7 (5.3) (Paste 13) (Ceramic Fiber 1) EX 5^(§)Yes 40 143.5 (5.4) (Paste 9) (Ceramic Fiber 0) CE G^(§) No 40 120.7(3.3) (Paste 12) (Ceramic Fiber 0) EX 8^(§) Yes 40  193.3 (17.1) (Paste15) (Ceramic Fiber 2) CE H^(§) No 40 196.5 (9.4) (Paste 16) (CeramicFiber 2) *Univeral (sculptable) formulations ^(§)Flowable formulations

The data in Table 6 demonstrates how fiber treatment impacts theflexural strength on the resultant cured composite. In the case ofuniversal composite formulations, flexural strength improved with silanesurface treatment of the ceramic fiber (i.e., EX 6 or EX 7 in comparisonto EX 1). Similarly, the flexural strength of cured flowable compositeformulations also improved (i.e., EX 8 or CE H in comparison to EX 5 orCE G).

Impact of Fiber-Filler-Resin Load

TABLE 7 Composite Material Formulations for Universal (Sculptable) andFlowable Dental Composites Containing Varying Levels of Ceramic FiberCeramic Fiber 2 and Silica/Zirconia Nanoclusters or Zirconia/SilicaFiller Composite Material S/T S/T S/T 20 nm S/T Zirconia/ Nano-zirconiaSilica Silica/Zirconia Silica Ceramic Ceramic Example (Ex)/Compar- Resin1 Resin 2

Nanoclusters Filler Fiber 2 Fiber 0 ative Example (CE) (wt. %) (wt. %)(wt. %) (wt. %) (wt. %) (wt. %) (wt. %) — (wt. %) — CE B* (Paste 5) 21.00.0 0.0 0.0 0.0 79.0 0.0 0.0 CE C* (Paste 6) 21.0 0.0 0.0 0.0 0.0 71.10.0 7.9 CE A* (Paste 1) 21.0 0.0 4.1 7.7 67.2 0.0 0.0 0.0 CE L* 20.0 0.03.5 6.5 70.0 0.0 0.0 0.0 CE M* 20.0 0.0 3.33 6.17 70.0 0.0 0.5 0.0 CE N*20.0 0.0 2.45 4.55 70.0 0.0 3.0 0.0 EX 1* (Paste 2) 21.0 0.0 3.9 7.463.7 0.0 0.0 4.0 EX 13* 20.0 0.0 1.75 3.25 70.0 0.0 5.0 0.0 EX 14* 25.00.0 1.75 3.25 20.0 0.0 50.0 0.0 EX 15* 20.0 0.0 3.5 6.5 20.0 0.0 50.00.0 CE O^(§) 0.0 35.0 4.9 4.9 55.2 0.0 0.0 0.0 CE P^(§) 0.0 35.0 0.0 0.010.0 0.0 55.0 — EX 16^(§) 0.0 40.0 5.35 5.35 42.9 0.0 6.4 0.0 EX 17^(§)0.0 40.0 0.0 0.0 17.1 0.0 42.9 0.0 EX 18^(§) 0.0 30.0 0.0 0.0 60.9 0.09.1 0.0 EX 19^(§) 0.0 30.0 2.3 2.3 18.7 0.0 46.7 0.0 EX 20^(§) 0.0 35.01.65 1.65 26.5 0.0 35.2 0.0 EX 21^(§) 0.0 30.0 0.0 0.0 20.0 0.0 50.0 0.0

 —Nanoparticle

TABLE 8 Flexural Strength, Flexural Modulus, and Polish Retention Datafor Selected Cured Composite Materials Ceramic Fiber 0 Fracture FlexuralFlexural Polish (F0) or Ceramic Toughness, Strength Modulus, RetentionExample (EX) and Compar- Nanocluster Fiber 2 (F2) MPa · m^(0.5) MPa GPa60° gloss unit ative Example (CE) filler? (wt. %) (Std. Dev.) (Std.Dev.) (Std. Dev.) (Std. Dev.) CE B* No F0 2.32 161.2 11.5 8.2 (0.0)(0.22) (5.0)  (0.4) (0.3) CE C* No F0 2.70 164.0 13.9 10.3  (7.9) (0.17)(11.0)  (0.3) (0.4) CE A* Yes F2 2.09 152.8 12.2 76.1  (0.0) (0.11)(7.4)  (0.3) (1.5) CE L* Yes F2 2.04 129.4 10.3 Not (0.0) (0.18) (8.7) (0.2) Tested CE M* Yes F2 2.15 132.2 11.7 Not (0.5) (0.04) (12.3) (0.9) Tested CE N* Yes F2 2.00 131.4 11.6 50.9  (3.0) (0.22) (3.5) (0.3) (4.9) EX 1* Yes F0 2.29 149.7 13.7 Not (4.0) (0.14) (10.9)  (0.3)tested EX 13* Yes F2 Not 136.1 12.6 Not (5.0) tested (3.4)  (0.2) TestedEX 14* Yes F2 2.91 135.4 16.4 30.3  (50.0)  (0.17) (16.2)  (1.2) (2.2)EX 15* Yes F2 3.22 125.6 19.2 Not (50.0)  (0.20) (16.7) (15)   Tested CEO^(§) Yes F2 1.49 126.4  7.9 53.2  (0.0) (0.10) (9.0)  (0.1) (8.2) CEP^(§) Yes F2 Not (55.0)  Tested EX 16^(§) Yes F2 1.62 125.3  8.2 55.9 (6.4) (0.09) (8.2)  (0.1) (3.4) EX 17^(§) Yes F2 2.19 179.0 14.6 36.0 (42.9)  (0.23) (11.4)  (0.4) (8.0) EX 18^(§) Yes F2 1.74 136.6 11.744.8  (9.1) (0.05) (11.7)  (0.3) (5.6) EX 19^(§) Yes F2 Not 138.3 15.424.6  (46.7)  Tested (15.4)  (0.6) (2.2) EX 20^(§) Yes F2 Not 185.4 15.237.2  (35.2)  Tested (15.2)  (0.3) (3.8) EX 21^(§) Yes F2 Not 92.1 16.4Not (50)   Tested (12.8)  (1.2) Tested *Univeral (sculptable)formulations ^(§)Flowable formulations

Impact of Ceramic Fiber Length

The length of the ceramic fiber impacts its efficacy at improvingmechanical properties. Table 9 describes the composite materialformulations containing blends of different ceramic fiber lengths (andlength distributions). EX 3 contained Ceramic Fiber 0 only (a relativelyshort-chopped fiber with a narrow length distribution), CE K containedCeramic Fiber 5 only (a relatively long-chopped fiber with a narrowlength distribution), while CE I and CE J contained blends of CeramicFiber 0 and Ceramic Fiber 6. Ceramic Fiber 0, Ceramic Fiber 5, andCeramic Fiber 6 were compositionally identical and lacked surfacetreatment. Table 10a describes the ceramic fiber length distributions,while Table 10b describes impact of fiber lengths and lengthdistributions on flexural strength and modulus, as well as fracturetoughness.

TABLE 9 Composite Material Formulations Containing Different Ceramicfiber Lengths S/T S/T 20 nm S/T Nanozirconia Silica Silica/ZirconiaCeramic Ceramic Ceramic Example (EX) and Compar- Resin 1 Nanoparicle

Nanoclusters Fiber 0 Fiber 6 Fiber 5 ative Example (CE) (wt. %) (wt. %)(wt. %) (wt. %) (wt. %) (wt. %) (wt. %) EX 3 21.0 3.3 6.2 53.7 15.8 0.00.0 EX 9 21.0 3.3 6.2 53.7 11.85 3.95 0.0 CE I 21.0 3.3 6.2 53.7 3.9511.85 0.0 CE J 21.0 3.3 6.2 53.7 0.0 15.8 0.0 CE K* 21.0 3.3 6.2 53.70.0 0.0 15.8

 —Nanoparticle *Ceramic Fiber 5 could not be dispersed in Resin 1 toprovide CE K a homogeneous paste (unacceptable clumping). Mechanicalproperties of the cured composite were not tested.

TABLE 10a Ceramic Fiber Length Impact on Properties EX 3 EX 9 CE I CE JCeramic Ceramic Ceramic Ceramic fiber fiber fiber fiber length lengthlength length (μm) (μm) (μm) (μm) L5 53.34 16.54 17.28 23.35 L10 105.8621.08 20.58 26.64 L15 119.73 24.52 23.36 29.70 L20 125.95 27.40 25.9031.79 L25 131.45 30.80 28.67 33.91 L30 136.13 33.93 31.18 36.36 L35139.24 36.99 33.43 38.45 L40 141.47 41.83 35.95 40.15 L45 144.32 45.4638.10 42.64 L50 146.53 51.65 40.33 44.70 L55 148.33 60.72 43.72 46.98L60 150.13 84.14 46.97 49.70 L65 152.15 117.14 49.66 52.21 L70 154.48133.17 55.18 55.79 L75 157.10 139.57 61.10 59.27 L80 159.70 147.26 69.0163.66 L85 163.28 151.22 99.23 68.66 L90 168.06 156.83 137.07 76.96 L95178.39 165.37 154.32 95.77 L99 288.61 186.03 170.09 137.82

TABLE 10b Ceramic Fiber Length Distribution Impact on MechanicalProperties Fracture Example (EX) and Flexural Flexural Toughness,Comparative Strength MPa Modulus, GPa MPa · m^(0.5) Example (CE) (Std.Dev.) (Std. Dev.) (Std. Dev.) EX 3  172.2 (10.3) 17.2 (0.2) 2.7 (0.12)EX 9 170.2 (3.9) 16.7 (0.2) 2.6 (0.17) CE I 153.3 (3.7) 14.5 (0.3) 2.5(0.05) CE J 152.2 (6.9) 14.2 (0.1) 2.3 (0.14)

As can be seen from Tables 10a and 10b, composite materials containingceramic fiber with an L50 of about greater than 50 micrometers and anL75 of greater than about 130 micrometers yield superior mechanicalproperties.

TABLE 11 Composite Material Formulations Containing Different Ceramicfiber Compositions IMPACT OF CERAMIC FIBER COMPOSITION CompositeMaterial S/T S/T 20 nm S/T Nanozirconia Silica Silica/Zirconia CeramicCeramic Ceramic Resin 1 Nanoparticle

Nanoclusters Fiber 2 Fiber 3 Fiber 4 (wt. %) (wt. %) (wt. %) (wt. %)(wt. %) wt % wt % Paste 21 21.5 4.1 7.7 51.0 15.7 0.0 0.0 Paste 22 21.54.1 7.7 51.0 0.0 0.0 15.7 Paste 23 21.5 4.1 7.7 51.0 0.0 15.7 0.0

 —Nanoparticle

In addition to improvements in mechanical properties, it is alsodesirable for the cured composite materials to polish to a high initialgloss using tools standard to the dental industry. To test this, polishselect cured composite materials according to the Polishability TestMethod. After polishing, measure the sixty degree gloss. Table 10summarizes the initial gloss results for cured composite materials of EX10, EX 11 and EX 12.

TABLE 12 Initial Gloss After Polishing for Cured Composite MaterialsExample (EX) Gloss (60° gloss) EX 10 (Paste 21) 59.2 (2.0) EX 12 (Paste22) 57.8 (0.1) EX 11 (Paste 23) 37.5 (0.8)

As seen in Table 10, cured composite materials containingaluminoborosilicate ceramic fibers (EX 10) or alumina-silica ceramicfibers (EX 12) polish to a higher initial gloss than cured compositematerials containing alumina ceramic fibers (EX 11). The initial 60°gloss obtained for EX 10 and EX 12 were particularly good, andapproached that of a commercially available dental composite material(FILTEK Supreme Ultra Universal Restorative available from 3M ESPE, St.Paul, Minn.).

Each of the Ceramic fiber and the cured composite materials have arefractive index, where if the refractive index values of these twocomponents match closely then the presence of the Ceramic fiber in thecured composite materials is less noticeable. The refractive index matchcan be demonstrated by measuring the contrast ratio of the curedcomposite material. As the contrast ratio is a measure of opticalopacity, the lower the contrast ratio the more light transmits throughthe cured composite material. A desirable contrast ratio value fordental applications for unpigmented or deep curing is typically a valueof about 55 or less. This allows for additional shading if desired.

The contrast ratio of EX 10, EX 11 and EX 12 were measured as describedabove in Contrast Ratio (CR) Test Method. Table 13 shows the results.

TABLE 13 Contrast Ratios Data for Cured Composite Materials ExampleContrast Ratio EX 10 (Paste 21) 41.7 EX 12 (Paste 22) 54.2 EX 11 (Paste23) 67.6

Various modifications and alterations to this disclosure will becomeapparent to those skilled in the art without departing from the scopeand spirit of this disclosure. It should be understood that thisdisclosure is not intended to be unduly limited by the illustrativeembodiments and examples set forth herein and that such examples andembodiments are presented by way of example only with the scope of thedisclosure intended to be limited only by the claims set forth herein.The complete disclosures of the patents, patent documents, andpublications cited herein are incorporated by reference in theirentirety as if each were individually incorporated.

1. A method of making a composite material, comprising: providing 20 to40 weight percent (wt. %) of a polymerizable component; providing 4 to50 wt. % of ceramic fibers; providing 20 to 70 wt. % of nanoclusters,where the wt. % values of the composite material are based on a totalweight of the composite material and total to a value of 100 wt. %, andwhere each of the ceramic fibers has a length and where the length offifty percent of the ceramic fibers, based on a total number of theceramic fibers, is at least 50 micrometers and the length of ninetypercent of the ceramic fibers, based on the total number of the ceramicfibers, is no greater than 500 micrometers; and admixing thepolymerizable component, the ceramic fibers and the nanoclusters to makethe composite material.
 2. The method of claim 1, where providing thecomposite material includes providing up to 12 wt. % of nanoparticlesbased on the total weight of the composite material, and admixing thepolymerizable component, the ceramic fibers and the nanoclusters and thenanoparticles to make the composite material.
 3. The method of claim 2,where providing the composite material includes providing 2 to 12 wt. %of nanoparticles based on the total weight of the composite material. 4.The method of claims 2, where the nanoparticles are discrete non-fumedmetal oxide nanoparticles.
 5. The method of claim 1, where providingnanoclusters includes providing 22 to 65 wt. % of nanoclusters.
 6. Themethod of claim 1, where providing ceramic fibers includes providing 4to 40 wt. % of the ceramic fibers based on the total weight of thecomposite material.
 7. The method of claim 1, where the length ofsixty-five percent of the ceramic fibers, based on a total number of theceramic fibers, is at least 100 micrometers and the length of ninetypercent of the ceramic fibers, based on the total number of the ceramicfibers, is no greater than 350 micrometers.
 8. The method of claim 1,where the ceramic fibers have an arithmetic mean diameter of 0.5 to 20micrometers.
 9. The method of claim 8, where the arithmetic meandiameter of the ceramic fibers is 9 to 12 micrometers.
 10. The method ofclaim 1, including hardening the polymerizable component to form ahardened polymerizable component having a refractive index, where theceramic fibers have a refractive index value within 0.1 or less of therefractive index of the hardened polymerizable component.
 11. The methodof claim 10, where the ceramic fibers have a refractive index within0.05 or less of the refractive index of the hardened polymerizablecomponent.
 12. The method of claim 1, where the ceramic fibers include asurface area and the method includes treating the ceramic fibers tochange the surface area of the ceramic fibers.
 13. The method of claim12, where the ceramic fibers include a predetermined amount of borontrioxide, and treating the ceramic fibers to change the surface area ofthe ceramic fibers includes removing at least a portion of the borontrioxide from the ceramic fibers.
 14. The method of claim 13, whereremoving at least a portion of the boron trioxide include boiling theceramic fibers in water to remove the boron trioxide in the ceramicfibers.
 15. The method of claim 1, further including hardening thecomposite material to form a dental product.
 16. The method of claim 1,where the nanoclusters are silica-zirconia nanoclusters.
 17. A method ofusing a composite material, comprising: placing a composite materialnear or on a tooth surface, wherein the composite material comprises 20to 40 weight percent (wt. %) of a polymerizable component; 4 to 50 wt. %of ceramic fibers; and 20 to 70 wt. % of nanoclusters, where the wt. %values of the composite material are based on a total weight of thecomposite material and total to a value of 100 wt. %, and where each ofthe ceramic fibers has a length and where the length of fifty percent ofthe ceramic fibers, based on a total number of the ceramic fibers, is atleast 50 micrometers and the length of ninety percent of the ceramicfibers, based on the total number of the ceramic fibers, is no greaterthan 500 micrometers; changing the shape of the composite material nearor on the tooth surface; and hardening the composite material.
 18. Themethod of claim 17, where changing the shape of the composite materialnear or on the tooth surface includes shaping the composite materialinto a dental product selected from the group consisting of a dentalprostheses, an orthodontic device, a dental crown, an anterior filling,a posterior filing or a cavity liner.
 19. The method of claim 17,further including polishing the composite material after hardening thecomposite material.